/* * Generic process-grouping system. * * Based originally on the cpuset system, extracted by Paul Menage * Copyright (C) 2006 Google, Inc * * Copyright notices from the original cpuset code: * -------------------------------------------------- * Copyright (C) 2003 BULL SA. * Copyright (C) 2004-2006 Silicon Graphics, Inc. * * Portions derived from Patrick Mochel's sysfs code. * sysfs is Copyright (c) 2001-3 Patrick Mochel * * 2003-10-10 Written by Simon Derr. * 2003-10-22 Updates by Stephen Hemminger. * 2004 May-July Rework by Paul Jackson. * --------------------------------------------------- * * This file is subject to the terms and conditions of the GNU General Public * License. See the file COPYING in the main directory of the Linux * distribution for more details. */ #include <linux/cgroup.h> #include <linux/errno.h> #include <linux/fs.h> #include <linux/kernel.h> #include <linux/list.h> #include <linux/mm.h> #include <linux/mutex.h> #include <linux/mount.h> #include <linux/pagemap.h> #include <linux/proc_fs.h> #include <linux/rcupdate.h> #include <linux/sched.h> #include <linux/backing-dev.h> #include <linux/seq_file.h> #include <linux/slab.h> #include <linux/magic.h> #include <linux/spinlock.h> #include <linux/string.h> #include <linux/sort.h> #include <linux/kmod.h> #include <linux/delayacct.h> #include <linux/cgroupstats.h> #include <asm/atomic.h> static DEFINE_MUTEX(cgroup_mutex); /* Generate an array of cgroup subsystem pointers */ #define SUBSYS(_x) &_x ## _subsys, static struct cgroup_subsys *subsys[] = { #include <linux/cgroup_subsys.h> }; /* * A cgroupfs_root represents the root of a cgroup hierarchy, * and may be associated with a superblock to form an active * hierarchy */ struct cgroupfs_root { struct super_block *sb; /* * The bitmask of subsystems intended to be attached to this * hierarchy */ unsigned long subsys_bits; /* The bitmask of subsystems currently attached to this hierarchy */ unsigned long actual_subsys_bits; /* A list running through the attached subsystems */ struct list_head subsys_list; /* The root cgroup for this hierarchy */ struct cgroup top_cgroup; /* Tracks how many cgroups are currently defined in hierarchy.*/ int number_of_cgroups; /* A list running through the mounted hierarchies */ struct list_head root_list; /* Hierarchy-specific flags */ unsigned long flags; /* The path to use for release notifications. No locking * between setting and use - so if userspace updates this * while child cgroups exist, you could miss a * notification. We ensure that it's always a valid * NUL-terminated string */ char release_agent_path[PATH_MAX]; }; /* * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the * subsystems that are otherwise unattached - it never has more than a * single cgroup, and all tasks are part of that cgroup. */ static struct cgroupfs_root rootnode; /* The list of hierarchy roots */ static LIST_HEAD(roots); static int root_count; /* dummytop is a shorthand for the dummy hierarchy's top cgroup */ #define dummytop (&rootnode.top_cgroup) /* This flag indicates whether tasks in the fork and exit paths should * take callback_mutex and check for fork/exit handlers to call. This * avoids us having to do extra work in the fork/exit path if none of the * subsystems need to be called. */ static int need_forkexit_callback; /* bits in struct cgroup flags field */ enum { /* Control Group is dead */ CGRP_REMOVED, /* Control Group has previously had a child cgroup or a task, * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set) */ CGRP_RELEASABLE, /* Control Group requires release notifications to userspace */ CGRP_NOTIFY_ON_RELEASE, }; /* convenient tests for these bits */ inline int cgroup_is_removed(const struct cgroup *cgrp) { return test_bit(CGRP_REMOVED, &cgrp->flags); } /* bits in struct cgroupfs_root flags field */ enum { ROOT_NOPREFIX, /* mounted subsystems have no named prefix */ }; inline int cgroup_is_releasable(const struct cgroup *cgrp) { const int bits = (1 << CGRP_RELEASABLE) | (1 << CGRP_NOTIFY_ON_RELEASE); return (cgrp->flags & bits) == bits; } inline int notify_on_release(const struct cgroup *cgrp) { return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); } /* * for_each_subsys() allows you to iterate on each subsystem attached to * an active hierarchy */ #define for_each_subsys(_root, _ss) \ list_for_each_entry(_ss, &_root->subsys_list, sibling) /* for_each_root() allows you to iterate across the active hierarchies */ #define for_each_root(_root) \ list_for_each_entry(_root, &roots, root_list) /* the list of cgroups eligible for automatic release. Protected by * release_list_lock */ static LIST_HEAD(release_list); static DEFINE_SPINLOCK(release_list_lock); static void cgroup_release_agent(struct work_struct *work); static DECLARE_WORK(release_agent_work, cgroup_release_agent); static void check_for_release(struct cgroup *cgrp); /* Link structure for associating css_set objects with cgroups */ struct cg_cgroup_link { /* * List running through cg_cgroup_links associated with a * cgroup, anchored on cgroup->css_sets */ struct list_head cgrp_link_list; /* * List running through cg_cgroup_links pointing at a * single css_set object, anchored on css_set->cg_links */ struct list_head cg_link_list; struct css_set *cg; }; /* The default css_set - used by init and its children prior to any * hierarchies being mounted. It contains a pointer to the root state * for each subsystem. Also used to anchor the list of css_sets. Not * reference-counted, to improve performance when child cgroups * haven't been created. */ static struct css_set init_css_set; static struct cg_cgroup_link init_css_set_link; /* css_set_lock protects the list of css_set objects, and the * chain of tasks off each css_set. Nests outside task->alloc_lock * due to cgroup_iter_start() */ static DEFINE_RWLOCK(css_set_lock); static int css_set_count; /* We don't maintain the lists running through each css_set to its * task until after the first call to cgroup_iter_start(). This * reduces the fork()/exit() overhead for people who have cgroups * compiled into their kernel but not actually in use */ static int use_task_css_set_links; /* When we create or destroy a css_set, the operation simply * takes/releases a reference count on all the cgroups referenced * by subsystems in this css_set. This can end up multiple-counting * some cgroups, but that's OK - the ref-count is just a * busy/not-busy indicator; ensuring that we only count each cgroup * once would require taking a global lock to ensure that no * subsystems moved between hierarchies while we were doing so. * * Possible TODO: decide at boot time based on the number of * registered subsystems and the number of CPUs or NUMA nodes whether * it's better for performance to ref-count every subsystem, or to * take a global lock and only add one ref count to each hierarchy. */ /* * unlink a css_set from the list and free it */ static void unlink_css_set(struct css_set *cg) { write_lock(&css_set_lock); list_del(&cg->list); css_set_count--; while (!list_empty(&cg->cg_links)) { struct cg_cgroup_link *link; link = list_entry(cg->cg_links.next, struct cg_cgroup_link, cg_link_list); list_del(&link->cg_link_list); list_del(&link->cgrp_link_list); kfree(link); } write_unlock(&css_set_lock); } static void __release_css_set(struct kref *k, int taskexit) { int i; struct css_set *cg = container_of(k, struct css_set, ref); unlink_css_set(cg); rcu_read_lock(); for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup *cgrp = cg->subsys[i]->cgroup; if (atomic_dec_and_test(&cgrp->count) && notify_on_release(cgrp)) { if (taskexit) set_bit(CGRP_RELEASABLE, &cgrp->flags); check_for_release(cgrp); } } rcu_read_unlock(); kfree(cg); } static void release_css_set(struct kref *k) { __release_css_set(k, 0); } static void release_css_set_taskexit(struct kref *k) { __release_css_set(k, 1); } /* * refcounted get/put for css_set objects */ static inline void get_css_set(struct css_set *cg) { kref_get(&cg->ref); } static inline void put_css_set(struct css_set *cg) { kref_put(&cg->ref, release_css_set); } static inline void put_css_set_taskexit(struct css_set *cg) { kref_put(&cg->ref, release_css_set_taskexit); } /* * find_existing_css_set() is a helper for * find_css_set(), and checks to see whether an existing * css_set is suitable. This currently walks a linked-list for * simplicity; a later patch will use a hash table for better * performance * * oldcg: the cgroup group that we're using before the cgroup * transition * * cgrp: the cgroup that we're moving into * * template: location in which to build the desired set of subsystem * state objects for the new cgroup group */ static struct css_set *find_existing_css_set( struct css_set *oldcg, struct cgroup *cgrp, struct cgroup_subsys_state *template[]) { int i; struct cgroupfs_root *root = cgrp->root; struct list_head *l = &init_css_set.list; /* Built the set of subsystem state objects that we want to * see in the new css_set */ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { if (root->subsys_bits & (1ull << i)) { /* Subsystem is in this hierarchy. So we want * the subsystem state from the new * cgroup */ template[i] = cgrp->subsys[i]; } else { /* Subsystem is not in this hierarchy, so we * don't want to change the subsystem state */ template[i] = oldcg->subsys[i]; } } /* Look through existing cgroup groups to find one to reuse */ do { struct css_set *cg = list_entry(l, struct css_set, list); if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) { /* All subsystems matched */ return cg; } /* Try the next cgroup group */ l = l->next; } while (l != &init_css_set.list); /* No existing cgroup group matched */ return NULL; } /* * allocate_cg_links() allocates "count" cg_cgroup_link structures * and chains them on tmp through their cgrp_link_list fields. Returns 0 on * success or a negative error */ static int allocate_cg_links(int count, struct list_head *tmp) { struct cg_cgroup_link *link; int i; INIT_LIST_HEAD(tmp); for (i = 0; i < count; i++) { link = kmalloc(sizeof(*link), GFP_KERNEL); if (!link) { while (!list_empty(tmp)) { link = list_entry(tmp->next, struct cg_cgroup_link, cgrp_link_list); list_del(&link->cgrp_link_list); kfree(link); } return -ENOMEM; } list_add(&link->cgrp_link_list, tmp); } return 0; } static void free_cg_links(struct list_head *tmp) { while (!list_empty(tmp)) { struct cg_cgroup_link *link; link = list_entry(tmp->next, struct cg_cgroup_link, cgrp_link_list); list_del(&link->cgrp_link_list); kfree(link); } } /* * find_css_set() takes an existing cgroup group and a * cgroup object, and returns a css_set object that's * equivalent to the old group, but with the given cgroup * substituted into the appropriate hierarchy. Must be called with * cgroup_mutex held */ static struct css_set *find_css_set( struct css_set *oldcg, struct cgroup *cgrp) { struct css_set *res; struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT]; int i; struct list_head tmp_cg_links; struct cg_cgroup_link *link; /* First see if we already have a cgroup group that matches * the desired set */ write_lock(&css_set_lock); res = find_existing_css_set(oldcg, cgrp, template); if (res) get_css_set(res); write_unlock(&css_set_lock); if (res) return res; res = kmalloc(sizeof(*res), GFP_KERNEL); if (!res) return NULL; /* Allocate all the cg_cgroup_link objects that we'll need */ if (allocate_cg_links(root_count, &tmp_cg_links) < 0) { kfree(res); return NULL; } kref_init(&res->ref); INIT_LIST_HEAD(&res->cg_links); INIT_LIST_HEAD(&res->tasks); /* Copy the set of subsystem state objects generated in * find_existing_css_set() */ memcpy(res->subsys, template, sizeof(res->subsys)); write_lock(&css_set_lock); /* Add reference counts and links from the new css_set. */ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup *cgrp = res->subsys[i]->cgroup; struct cgroup_subsys *ss = subsys[i]; atomic_inc(&cgrp->count); /* * We want to add a link once per cgroup, so we * only do it for the first subsystem in each * hierarchy */ if (ss->root->subsys_list.next == &ss->sibling) { BUG_ON(list_empty(&tmp_cg_links)); link = list_entry(tmp_cg_links.next, struct cg_cgroup_link, cgrp_link_list); list_del(&link->cgrp_link_list); list_add(&link->cgrp_link_list, &cgrp->css_sets); link->cg = res; list_add(&link->cg_link_list, &res->cg_links); } } if (list_empty(&rootnode.subsys_list)) { link = list_entry(tmp_cg_links.next, struct cg_cgroup_link, cgrp_link_list); list_del(&link->cgrp_link_list); list_add(&link->cgrp_link_list, &dummytop->css_sets); link->cg = res; list_add(&link->cg_link_list, &res->cg_links); } BUG_ON(!list_empty(&tmp_cg_links)); /* Link this cgroup group into the list */ list_add(&res->list, &init_css_set.list); css_set_count++; INIT_LIST_HEAD(&res->tasks); write_unlock(&css_set_lock); return res; } /* * There is one global cgroup mutex. We also require taking * task_lock() when dereferencing a task's cgroup subsys pointers. * See "The task_lock() exception", at the end of this comment. * * A task must hold cgroup_mutex to modify cgroups. * * Any task can increment and decrement the count field without lock. * So in general, code holding cgroup_mutex can't rely on the count * field not changing. However, if the count goes to zero, then only * attach_task() can increment it again. Because a count of zero * means that no tasks are currently attached, therefore there is no * way a task attached to that cgroup can fork (the other way to * increment the count). So code holding cgroup_mutex can safely * assume that if the count is zero, it will stay zero. Similarly, if * a task holds cgroup_mutex on a cgroup with zero count, it * knows that the cgroup won't be removed, as cgroup_rmdir() * needs that mutex. * * The cgroup_common_file_write handler for operations that modify * the cgroup hierarchy holds cgroup_mutex across the entire operation, * single threading all such cgroup modifications across the system. * * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't * (usually) take cgroup_mutex. These are the two most performance * critical pieces of code here. The exception occurs on cgroup_exit(), * when a task in a notify_on_release cgroup exits. Then cgroup_mutex * is taken, and if the cgroup count is zero, a usermode call made * to /sbin/cgroup_release_agent with the name of the cgroup (path * relative to the root of cgroup file system) as the argument. * * A cgroup can only be deleted if both its 'count' of using tasks * is zero, and its list of 'children' cgroups is empty. Since all * tasks in the system use _some_ cgroup, and since there is always at * least one task in the system (init, pid == 1), therefore, top_cgroup * always has either children cgroups and/or using tasks. So we don't * need a special hack to ensure that top_cgroup cannot be deleted. * * The task_lock() exception * * The need for this exception arises from the action of * attach_task(), which overwrites one tasks cgroup pointer with * another. It does so using cgroup_mutexe, however there are * several performance critical places that need to reference * task->cgroup without the expense of grabbing a system global * mutex. Therefore except as noted below, when dereferencing or, as * in attach_task(), modifying a task'ss cgroup pointer we use * task_lock(), which acts on a spinlock (task->alloc_lock) already in * the task_struct routinely used for such matters. * * P.S. One more locking exception. RCU is used to guard the * update of a tasks cgroup pointer by attach_task() */ /** * cgroup_lock - lock out any changes to cgroup structures * */ void cgroup_lock(void) { mutex_lock(&cgroup_mutex); } /** * cgroup_unlock - release lock on cgroup changes * * Undo the lock taken in a previous cgroup_lock() call. */ void cgroup_unlock(void) { mutex_unlock(&cgroup_mutex); } /* * A couple of forward declarations required, due to cyclic reference loop: * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir -> * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations * -> cgroup_mkdir. */ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode); static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry); static int cgroup_populate_dir(struct cgroup *cgrp); static struct inode_operations cgroup_dir_inode_operations; static struct file_operations proc_cgroupstats_operations; static struct backing_dev_info cgroup_backing_dev_info = { .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK, }; static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb) { struct inode *inode = new_inode(sb); if (inode) { inode->i_mode = mode; inode->i_uid = current->fsuid; inode->i_gid = current->fsgid; inode->i_blocks = 0; inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info; } return inode; } static void cgroup_diput(struct dentry *dentry, struct inode *inode) { /* is dentry a directory ? if so, kfree() associated cgroup */ if (S_ISDIR(inode->i_mode)) { struct cgroup *cgrp = dentry->d_fsdata; BUG_ON(!(cgroup_is_removed(cgrp))); /* It's possible for external users to be holding css * reference counts on a cgroup; css_put() needs to * be able to access the cgroup after decrementing * the reference count in order to know if it needs to * queue the cgroup to be handled by the release * agent */ synchronize_rcu(); kfree(cgrp); } iput(inode); } static void remove_dir(struct dentry *d) { struct dentry *parent = dget(d->d_parent); d_delete(d); simple_rmdir(parent->d_inode, d); dput(parent); } static void cgroup_clear_directory(struct dentry *dentry) { struct list_head *node; BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex)); spin_lock(&dcache_lock); node = dentry->d_subdirs.next; while (node != &dentry->d_subdirs) { struct dentry *d = list_entry(node, struct dentry, d_u.d_child); list_del_init(node); if (d->d_inode) { /* This should never be called on a cgroup * directory with child cgroups */ BUG_ON(d->d_inode->i_mode & S_IFDIR); d = dget_locked(d); spin_unlock(&dcache_lock); d_delete(d); simple_unlink(dentry->d_inode, d); dput(d); spin_lock(&dcache_lock); } node = dentry->d_subdirs.next; } spin_unlock(&dcache_lock); } /* * NOTE : the dentry must have been dget()'ed */ static void cgroup_d_remove_dir(struct dentry *dentry) { cgroup_clear_directory(dentry); spin_lock(&dcache_lock); list_del_init(&dentry->d_u.d_child); spin_unlock(&dcache_lock); remove_dir(dentry); } static int rebind_subsystems(struct cgroupfs_root *root, unsigned long final_bits) { unsigned long added_bits, removed_bits; struct cgroup *cgrp = &root->top_cgroup; int i; removed_bits = root->actual_subsys_bits & ~final_bits; added_bits = final_bits & ~root->actual_subsys_bits; /* Check that any added subsystems are currently free */ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { unsigned long long bit = 1ull << i; struct cgroup_subsys *ss = subsys[i]; if (!(bit & added_bits)) continue; if (ss->root != &rootnode) { /* Subsystem isn't free */ return -EBUSY; } } /* Currently we don't handle adding/removing subsystems when * any child cgroups exist. This is theoretically supportable * but involves complex error handling, so it's being left until * later */ if (!list_empty(&cgrp->children)) return -EBUSY; /* Process each subsystem */ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; unsigned long bit = 1UL << i; if (bit & added_bits) { /* We're binding this subsystem to this hierarchy */ BUG_ON(cgrp->subsys[i]); BUG_ON(!dummytop->subsys[i]); BUG_ON(dummytop->subsys[i]->cgroup != dummytop); cgrp->subsys[i] = dummytop->subsys[i]; cgrp->subsys[i]->cgroup = cgrp; list_add(&ss->sibling, &root->subsys_list); rcu_assign_pointer(ss->root, root); if (ss->bind) ss->bind(ss, cgrp); } else if (bit & removed_bits) { /* We're removing this subsystem */ BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]); BUG_ON(cgrp->subsys[i]->cgroup != cgrp); if (ss->bind) ss->bind(ss, dummytop); dummytop->subsys[i]->cgroup = dummytop; cgrp->subsys[i] = NULL; rcu_assign_pointer(subsys[i]->root, &rootnode); list_del(&ss->sibling); } else if (bit & final_bits) { /* Subsystem state should already exist */ BUG_ON(!cgrp->subsys[i]); } else { /* Subsystem state shouldn't exist */ BUG_ON(cgrp->subsys[i]); } } root->subsys_bits = root->actual_subsys_bits = final_bits; synchronize_rcu(); return 0; } static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs) { struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info; struct cgroup_subsys *ss; mutex_lock(&cgroup_mutex); for_each_subsys(root, ss) seq_printf(seq, ",%s", ss->name); if (test_bit(ROOT_NOPREFIX, &root->flags)) seq_puts(seq, ",noprefix"); if (strlen(root->release_agent_path)) seq_printf(seq, ",release_agent=%s", root->release_agent_path); mutex_unlock(&cgroup_mutex); return 0; } struct cgroup_sb_opts { unsigned long subsys_bits; unsigned long flags; char *release_agent; }; /* Convert a hierarchy specifier into a bitmask of subsystems and * flags. */ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) { char *token, *o = data ?: "all"; opts->subsys_bits = 0; opts->flags = 0; opts->release_agent = NULL; while ((token = strsep(&o, ",")) != NULL) { if (!*token) return -EINVAL; if (!strcmp(token, "all")) { opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1; } else if (!strcmp(token, "noprefix")) { set_bit(ROOT_NOPREFIX, &opts->flags); } else if (!strncmp(token, "release_agent=", 14)) { /* Specifying two release agents is forbidden */ if (opts->release_agent) return -EINVAL; opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL); if (!opts->release_agent) return -ENOMEM; strncpy(opts->release_agent, token + 14, PATH_MAX - 1); opts->release_agent[PATH_MAX - 1] = 0; } else { struct cgroup_subsys *ss; int i; for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { ss = subsys[i]; if (!strcmp(token, ss->name)) { set_bit(i, &opts->subsys_bits); break; } } if (i == CGROUP_SUBSYS_COUNT) return -ENOENT; } } /* We can't have an empty hierarchy */ if (!opts->subsys_bits) return -EINVAL; return 0; } static int cgroup_remount(struct super_block *sb, int *flags, char *data) { int ret = 0; struct cgroupfs_root *root = sb->s_fs_info; struct cgroup *cgrp = &root->top_cgroup; struct cgroup_sb_opts opts; mutex_lock(&cgrp->dentry->d_inode->i_mutex); mutex_lock(&cgroup_mutex); /* See what subsystems are wanted */ ret = parse_cgroupfs_options(data, &opts); if (ret) goto out_unlock; /* Don't allow flags to change at remount */ if (opts.flags != root->flags) { ret = -EINVAL; goto out_unlock; } ret = rebind_subsystems(root, opts.subsys_bits); /* (re)populate subsystem files */ if (!ret) cgroup_populate_dir(cgrp); if (opts.release_agent) strcpy(root->release_agent_path, opts.release_agent); out_unlock: if (opts.release_agent) kfree(opts.release_agent); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgrp->dentry->d_inode->i_mutex); return ret; } static struct super_operations cgroup_ops = { .statfs = simple_statfs, .drop_inode = generic_delete_inode, .show_options = cgroup_show_options, .remount_fs = cgroup_remount, }; static void init_cgroup_root(struct cgroupfs_root *root) { struct cgroup *cgrp = &root->top_cgroup; INIT_LIST_HEAD(&root->subsys_list); INIT_LIST_HEAD(&root->root_list); root->number_of_cgroups = 1; cgrp->root = root; cgrp->top_cgroup = cgrp; INIT_LIST_HEAD(&cgrp->sibling); INIT_LIST_HEAD(&cgrp->children); INIT_LIST_HEAD(&cgrp->css_sets); INIT_LIST_HEAD(&cgrp->release_list); } static int cgroup_test_super(struct super_block *sb, void *data) { struct cgroupfs_root *new = data; struct cgroupfs_root *root = sb->s_fs_info; /* First check subsystems */ if (new->subsys_bits != root->subsys_bits) return 0; /* Next check flags */ if (new->flags != root->flags) return 0; return 1; } static int cgroup_set_super(struct super_block *sb, void *data) { int ret; struct cgroupfs_root *root = data; ret = set_anon_super(sb, NULL); if (ret) return ret; sb->s_fs_info = root; root->sb = sb; sb->s_blocksize = PAGE_CACHE_SIZE; sb->s_blocksize_bits = PAGE_CACHE_SHIFT; sb->s_magic = CGROUP_SUPER_MAGIC; sb->s_op = &cgroup_ops; return 0; } static int cgroup_get_rootdir(struct super_block *sb) { struct inode *inode = cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb); struct dentry *dentry; if (!inode) return -ENOMEM; inode->i_op = &simple_dir_inode_operations; inode->i_fop = &simple_dir_operations; inode->i_op = &cgroup_dir_inode_operations; /* directories start off with i_nlink == 2 (for "." entry) */ inc_nlink(inode); dentry = d_alloc_root(inode); if (!dentry) { iput(inode); return -ENOMEM; } sb->s_root = dentry; return 0; } static int cgroup_get_sb(struct file_system_type *fs_type, int flags, const char *unused_dev_name, void *data, struct vfsmount *mnt) { struct cgroup_sb_opts opts; int ret = 0; struct super_block *sb; struct cgroupfs_root *root; struct list_head tmp_cg_links, *l; INIT_LIST_HEAD(&tmp_cg_links); /* First find the desired set of subsystems */ ret = parse_cgroupfs_options(data, &opts); if (ret) { if (opts.release_agent) kfree(opts.release_agent); return ret; } root = kzalloc(sizeof(*root), GFP_KERNEL); if (!root) return -ENOMEM; init_cgroup_root(root); root->subsys_bits = opts.subsys_bits; root->flags = opts.flags; if (opts.release_agent) { strcpy(root->release_agent_path, opts.release_agent); kfree(opts.release_agent); } sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root); if (IS_ERR(sb)) { kfree(root); return PTR_ERR(sb); } if (sb->s_fs_info != root) { /* Reusing an existing superblock */ BUG_ON(sb->s_root == NULL); kfree(root); root = NULL; } else { /* New superblock */ struct cgroup *cgrp = &root->top_cgroup; struct inode *inode; BUG_ON(sb->s_root != NULL); ret = cgroup_get_rootdir(sb); if (ret) goto drop_new_super; inode = sb->s_root->d_inode; mutex_lock(&inode->i_mutex); mutex_lock(&cgroup_mutex); /* * We're accessing css_set_count without locking * css_set_lock here, but that's OK - it can only be * increased by someone holding cgroup_lock, and * that's us. The worst that can happen is that we * have some link structures left over */ ret = allocate_cg_links(css_set_count, &tmp_cg_links); if (ret) { mutex_unlock(&cgroup_mutex); mutex_unlock(&inode->i_mutex); goto drop_new_super; } ret = rebind_subsystems(root, root->subsys_bits); if (ret == -EBUSY) { mutex_unlock(&cgroup_mutex); mutex_unlock(&inode->i_mutex); goto drop_new_super; } /* EBUSY should be the only error here */ BUG_ON(ret); list_add(&root->root_list, &roots); root_count++; sb->s_root->d_fsdata = &root->top_cgroup; root->top_cgroup.dentry = sb->s_root; /* Link the top cgroup in this hierarchy into all * the css_set objects */ write_lock(&css_set_lock); l = &init_css_set.list; do { struct css_set *cg; struct cg_cgroup_link *link; cg = list_entry(l, struct css_set, list); BUG_ON(list_empty(&tmp_cg_links)); link = list_entry(tmp_cg_links.next, struct cg_cgroup_link, cgrp_link_list); list_del(&link->cgrp_link_list); link->cg = cg; list_add(&link->cgrp_link_list, &root->top_cgroup.css_sets); list_add(&link->cg_link_list, &cg->cg_links); l = l->next; } while (l != &init_css_set.list); write_unlock(&css_set_lock); free_cg_links(&tmp_cg_links); BUG_ON(!list_empty(&cgrp->sibling)); BUG_ON(!list_empty(&cgrp->children)); BUG_ON(root->number_of_cgroups != 1); cgroup_populate_dir(cgrp); mutex_unlock(&inode->i_mutex); mutex_unlock(&cgroup_mutex); } return simple_set_mnt(mnt, sb); drop_new_super: up_write(&sb->s_umount); deactivate_super(sb); free_cg_links(&tmp_cg_links); return ret; } static void cgroup_kill_sb(struct super_block *sb) { struct cgroupfs_root *root = sb->s_fs_info; struct cgroup *cgrp = &root->top_cgroup; int ret; BUG_ON(!root); BUG_ON(root->number_of_cgroups != 1); BUG_ON(!list_empty(&cgrp->children)); BUG_ON(!list_empty(&cgrp->sibling)); mutex_lock(&cgroup_mutex); /* Rebind all subsystems back to the default hierarchy */ ret = rebind_subsystems(root, 0); /* Shouldn't be able to fail ... */ BUG_ON(ret); /* * Release all the links from css_sets to this hierarchy's * root cgroup */ write_lock(&css_set_lock); while (!list_empty(&cgrp->css_sets)) { struct cg_cgroup_link *link; link = list_entry(cgrp->css_sets.next, struct cg_cgroup_link, cgrp_link_list); list_del(&link->cg_link_list); list_del(&link->cgrp_link_list); kfree(link); } write_unlock(&css_set_lock); if (!list_empty(&root->root_list)) { list_del(&root->root_list); root_count--; } mutex_unlock(&cgroup_mutex); kfree(root); kill_litter_super(sb); } static struct file_system_type cgroup_fs_type = { .name = "cgroup", .get_sb = cgroup_get_sb, .kill_sb = cgroup_kill_sb, }; static inline struct cgroup *__d_cgrp(struct dentry *dentry) { return dentry->d_fsdata; } static inline struct cftype *__d_cft(struct dentry *dentry) { return dentry->d_fsdata; } /* * Called with cgroup_mutex held. Writes path of cgroup into buf. * Returns 0 on success, -errno on error. */ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) { char *start; if (cgrp == dummytop) { /* * Inactive subsystems have no dentry for their root * cgroup */ strcpy(buf, "/"); return 0; } start = buf + buflen; *--start = '\0'; for (;;) { int len = cgrp->dentry->d_name.len; if ((start -= len) < buf) return -ENAMETOOLONG; memcpy(start, cgrp->dentry->d_name.name, len); cgrp = cgrp->parent; if (!cgrp) break; if (!cgrp->parent) continue; if (--start < buf) return -ENAMETOOLONG; *start = '/'; } memmove(buf, start, buf + buflen - start); return 0; } /* * Return the first subsystem attached to a cgroup's hierarchy, and * its subsystem id. */ static void get_first_subsys(const struct cgroup *cgrp, struct cgroup_subsys_state **css, int *subsys_id) { const struct cgroupfs_root *root = cgrp->root; const struct cgroup_subsys *test_ss; BUG_ON(list_empty(&root->subsys_list)); test_ss = list_entry(root->subsys_list.next, struct cgroup_subsys, sibling); if (css) { *css = cgrp->subsys[test_ss->subsys_id]; BUG_ON(!*css); } if (subsys_id) *subsys_id = test_ss->subsys_id; } /* * Attach task 'tsk' to cgroup 'cgrp' * * Call holding cgroup_mutex. May take task_lock of * the task 'pid' during call. */ static int attach_task(struct cgroup *cgrp, struct task_struct *tsk) { int retval = 0; struct cgroup_subsys *ss; struct cgroup *oldcgrp; struct css_set *cg = tsk->cgroups; struct css_set *newcg; struct cgroupfs_root *root = cgrp->root; int subsys_id; get_first_subsys(cgrp, NULL, &subsys_id); /* Nothing to do if the task is already in that cgroup */ oldcgrp = task_cgroup(tsk, subsys_id); if (cgrp == oldcgrp) return 0; for_each_subsys(root, ss) { if (ss->can_attach) { retval = ss->can_attach(ss, cgrp, tsk); if (retval) { return retval; } } } /* * Locate or allocate a new css_set for this task, * based on its final set of cgroups */ newcg = find_css_set(cg, cgrp); if (!newcg) { return -ENOMEM; } task_lock(tsk); if (tsk->flags & PF_EXITING) { task_unlock(tsk); put_css_set(newcg); return -ESRCH; } rcu_assign_pointer(tsk->cgroups, newcg); task_unlock(tsk); /* Update the css_set linked lists if we're using them */ write_lock(&css_set_lock); if (!list_empty(&tsk->cg_list)) { list_del(&tsk->cg_list); list_add(&tsk->cg_list, &newcg->tasks); } write_unlock(&css_set_lock); for_each_subsys(root, ss) { if (ss->attach) { ss->attach(ss, cgrp, oldcgrp, tsk); } } set_bit(CGRP_RELEASABLE, &oldcgrp->flags); synchronize_rcu(); put_css_set(cg); return 0; } /* * Attach task with pid 'pid' to cgroup 'cgrp'. Call with * cgroup_mutex, may take task_lock of task */ static int attach_task_by_pid(struct cgroup *cgrp, char *pidbuf) { pid_t pid; struct task_struct *tsk; int ret; if (sscanf(pidbuf, "%d", &pid) != 1) return -EIO; if (pid) { rcu_read_lock(); tsk = find_task_by_pid(pid); if (!tsk || tsk->flags & PF_EXITING) { rcu_read_unlock(); return -ESRCH; } get_task_struct(tsk); rcu_read_unlock(); if ((current->euid) && (current->euid != tsk->uid) && (current->euid != tsk->suid)) { put_task_struct(tsk); return -EACCES; } } else { tsk = current; get_task_struct(tsk); } ret = attach_task(cgrp, tsk); put_task_struct(tsk); return ret; } /* The various types of files and directories in a cgroup file system */ enum cgroup_filetype { FILE_ROOT, FILE_DIR, FILE_TASKLIST, FILE_NOTIFY_ON_RELEASE, FILE_RELEASABLE, FILE_RELEASE_AGENT, }; static ssize_t cgroup_write_uint(struct cgroup *cgrp, struct cftype *cft, struct file *file, const char __user *userbuf, size_t nbytes, loff_t *unused_ppos) { char buffer[64]; int retval = 0; u64 val; char *end; if (!nbytes) return -EINVAL; if (nbytes >= sizeof(buffer)) return -E2BIG; if (copy_from_user(buffer, userbuf, nbytes)) return -EFAULT; buffer[nbytes] = 0; /* nul-terminate */ /* strip newline if necessary */ if (nbytes && (buffer[nbytes-1] == '\n')) buffer[nbytes-1] = 0; val = simple_strtoull(buffer, &end, 0); if (*end) return -EINVAL; /* Pass to subsystem */ retval = cft->write_uint(cgrp, cft, val); if (!retval) retval = nbytes; return retval; } static ssize_t cgroup_common_file_write(struct cgroup *cgrp, struct cftype *cft, struct file *file, const char __user *userbuf, size_t nbytes, loff_t *unused_ppos) { enum cgroup_filetype type = cft->private; char *buffer; int retval = 0; if (nbytes >= PATH_MAX) return -E2BIG; /* +1 for nul-terminator */ buffer = kmalloc(nbytes + 1, GFP_KERNEL); if (buffer == NULL) return -ENOMEM; if (copy_from_user(buffer, userbuf, nbytes)) { retval = -EFAULT; goto out1; } buffer[nbytes] = 0; /* nul-terminate */ mutex_lock(&cgroup_mutex); if (cgroup_is_removed(cgrp)) { retval = -ENODEV; goto out2; } switch (type) { case FILE_TASKLIST: retval = attach_task_by_pid(cgrp, buffer); break; case FILE_NOTIFY_ON_RELEASE: clear_bit(CGRP_RELEASABLE, &cgrp->flags); if (simple_strtoul(buffer, NULL, 10) != 0) set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); else clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); break; case FILE_RELEASE_AGENT: { struct cgroupfs_root *root = cgrp->root; /* Strip trailing newline */ if (nbytes && (buffer[nbytes-1] == '\n')) { buffer[nbytes-1] = 0; } if (nbytes < sizeof(root->release_agent_path)) { /* We never write anything other than '\0' * into the last char of release_agent_path, * so it always remains a NUL-terminated * string */ strncpy(root->release_agent_path, buffer, nbytes); root->release_agent_path[nbytes] = 0; } else { retval = -ENOSPC; } break; } default: retval = -EINVAL; goto out2; } if (retval == 0) retval = nbytes; out2: mutex_unlock(&cgroup_mutex); out1: kfree(buffer); return retval; } static ssize_t cgroup_file_write(struct file *file, const char __user *buf, size_t nbytes, loff_t *ppos) { struct cftype *cft = __d_cft(file->f_dentry); struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent); if (!cft) return -ENODEV; if (cft->write) return cft->write(cgrp, cft, file, buf, nbytes, ppos); if (cft->write_uint) return cgroup_write_uint(cgrp, cft, file, buf, nbytes, ppos); return -EINVAL; } static ssize_t cgroup_read_uint(struct cgroup *cgrp, struct cftype *cft, struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { char tmp[64]; u64 val = cft->read_uint(cgrp, cft); int len = sprintf(tmp, "%llu\n", (unsigned long long) val); return simple_read_from_buffer(buf, nbytes, ppos, tmp, len); } static ssize_t cgroup_common_file_read(struct cgroup *cgrp, struct cftype *cft, struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { enum cgroup_filetype type = cft->private; char *page; ssize_t retval = 0; char *s; if (!(page = (char *)__get_free_page(GFP_KERNEL))) return -ENOMEM; s = page; switch (type) { case FILE_RELEASE_AGENT: { struct cgroupfs_root *root; size_t n; mutex_lock(&cgroup_mutex); root = cgrp->root; n = strnlen(root->release_agent_path, sizeof(root->release_agent_path)); n = min(n, (size_t) PAGE_SIZE); strncpy(s, root->release_agent_path, n); mutex_unlock(&cgroup_mutex); s += n; break; } default: retval = -EINVAL; goto out; } *s++ = '\n'; retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page); out: free_page((unsigned long)page); return retval; } static ssize_t cgroup_file_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { struct cftype *cft = __d_cft(file->f_dentry); struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent); if (!cft) return -ENODEV; if (cft->read) return cft->read(cgrp, cft, file, buf, nbytes, ppos); if (cft->read_uint) return cgroup_read_uint(cgrp, cft, file, buf, nbytes, ppos); return -EINVAL; } static int cgroup_file_open(struct inode *inode, struct file *file) { int err; struct cftype *cft; err = generic_file_open(inode, file); if (err) return err; cft = __d_cft(file->f_dentry); if (!cft) return -ENODEV; if (cft->open) err = cft->open(inode, file); else err = 0; return err; } static int cgroup_file_release(struct inode *inode, struct file *file) { struct cftype *cft = __d_cft(file->f_dentry); if (cft->release) return cft->release(inode, file); return 0; } /* * cgroup_rename - Only allow simple rename of directories in place. */ static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry) { if (!S_ISDIR(old_dentry->d_inode->i_mode)) return -ENOTDIR; if (new_dentry->d_inode) return -EEXIST; if (old_dir != new_dir) return -EIO; return simple_rename(old_dir, old_dentry, new_dir, new_dentry); } static struct file_operations cgroup_file_operations = { .read = cgroup_file_read, .write = cgroup_file_write, .llseek = generic_file_llseek, .open = cgroup_file_open, .release = cgroup_file_release, }; static struct inode_operations cgroup_dir_inode_operations = { .lookup = simple_lookup, .mkdir = cgroup_mkdir, .rmdir = cgroup_rmdir, .rename = cgroup_rename, }; static int cgroup_create_file(struct dentry *dentry, int mode, struct super_block *sb) { static struct dentry_operations cgroup_dops = { .d_iput = cgroup_diput, }; struct inode *inode; if (!dentry) return -ENOENT; if (dentry->d_inode) return -EEXIST; inode = cgroup_new_inode(mode, sb); if (!inode) return -ENOMEM; if (S_ISDIR(mode)) { inode->i_op = &cgroup_dir_inode_operations; inode->i_fop = &simple_dir_operations; /* start off with i_nlink == 2 (for "." entry) */ inc_nlink(inode); /* start with the directory inode held, so that we can * populate it without racing with another mkdir */ mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD); } else if (S_ISREG(mode)) { inode->i_size = 0; inode->i_fop = &cgroup_file_operations; } dentry->d_op = &cgroup_dops; d_instantiate(dentry, inode); dget(dentry); /* Extra count - pin the dentry in core */ return 0; } /* * cgroup_create_dir - create a directory for an object. * cgrp: the cgroup we create the directory for. * It must have a valid ->parent field * And we are going to fill its ->dentry field. * dentry: dentry of the new cgroup * mode: mode to set on new directory. */ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry, int mode) { struct dentry *parent; int error = 0; parent = cgrp->parent->dentry; error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb); if (!error) { dentry->d_fsdata = cgrp; inc_nlink(parent->d_inode); cgrp->dentry = dentry; dget(dentry); } dput(dentry); return error; } int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys, const struct cftype *cft) { struct dentry *dir = cgrp->dentry; struct dentry *dentry; int error; char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 }; if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) { strcpy(name, subsys->name); strcat(name, "."); } strcat(name, cft->name); BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex)); dentry = lookup_one_len(name, dir, strlen(name)); if (!IS_ERR(dentry)) { error = cgroup_create_file(dentry, 0644 | S_IFREG, cgrp->root->sb); if (!error) dentry->d_fsdata = (void *)cft; dput(dentry); } else error = PTR_ERR(dentry); return error; } int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys, const struct cftype cft[], int count) { int i, err; for (i = 0; i < count; i++) { err = cgroup_add_file(cgrp, subsys, &cft[i]); if (err) return err; } return 0; } /* Count the number of tasks in a cgroup. */ int cgroup_task_count(const struct cgroup *cgrp) { int count = 0; struct list_head *l; read_lock(&css_set_lock); l = cgrp->css_sets.next; while (l != &cgrp->css_sets) { struct cg_cgroup_link *link = list_entry(l, struct cg_cgroup_link, cgrp_link_list); count += atomic_read(&link->cg->ref.refcount); l = l->next; } read_unlock(&css_set_lock); return count; } /* * Advance a list_head iterator. The iterator should be positioned at * the start of a css_set */ static void cgroup_advance_iter(struct cgroup *cgrp, struct cgroup_iter *it) { struct list_head *l = it->cg_link; struct cg_cgroup_link *link; struct css_set *cg; /* Advance to the next non-empty css_set */ do { l = l->next; if (l == &cgrp->css_sets) { it->cg_link = NULL; return; } link = list_entry(l, struct cg_cgroup_link, cgrp_link_list); cg = link->cg; } while (list_empty(&cg->tasks)); it->cg_link = l; it->task = cg->tasks.next; } void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it) { /* * The first time anyone tries to iterate across a cgroup, * we need to enable the list linking each css_set to its * tasks, and fix up all existing tasks. */ if (!use_task_css_set_links) { struct task_struct *p, *g; write_lock(&css_set_lock); use_task_css_set_links = 1; do_each_thread(g, p) { task_lock(p); if (list_empty(&p->cg_list)) list_add(&p->cg_list, &p->cgroups->tasks); task_unlock(p); } while_each_thread(g, p); write_unlock(&css_set_lock); } read_lock(&css_set_lock); it->cg_link = &cgrp->css_sets; cgroup_advance_iter(cgrp, it); } struct task_struct *cgroup_iter_next(struct cgroup *cgrp, struct cgroup_iter *it) { struct task_struct *res; struct list_head *l = it->task; /* If the iterator cg is NULL, we have no tasks */ if (!it->cg_link) return NULL; res = list_entry(l, struct task_struct, cg_list); /* Advance iterator to find next entry */ l = l->next; if (l == &res->cgroups->tasks) { /* We reached the end of this task list - move on to * the next cg_cgroup_link */ cgroup_advance_iter(cgrp, it); } else { it->task = l; } return res; } void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it) { read_unlock(&css_set_lock); } /* * Stuff for reading the 'tasks' file. * * Reading this file can return large amounts of data if a cgroup has * *lots* of attached tasks. So it may need several calls to read(), * but we cannot guarantee that the information we produce is correct * unless we produce it entirely atomically. * * Upon tasks file open(), a struct ctr_struct is allocated, that * will have a pointer to an array (also allocated here). The struct * ctr_struct * is stored in file->private_data. Its resources will * be freed by release() when the file is closed. The array is used * to sprintf the PIDs and then used by read(). */ struct ctr_struct { char *buf; int bufsz; }; /* * Load into 'pidarray' up to 'npids' of the tasks using cgroup * 'cgrp'. Return actual number of pids loaded. No need to * task_lock(p) when reading out p->cgroup, since we're in an RCU * read section, so the css_set can't go away, and is * immutable after creation. */ static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cgrp) { int n = 0; struct cgroup_iter it; struct task_struct *tsk; cgroup_iter_start(cgrp, &it); while ((tsk = cgroup_iter_next(cgrp, &it))) { if (unlikely(n == npids)) break; pidarray[n++] = task_pid_nr(tsk); } cgroup_iter_end(cgrp, &it); return n; } /** * Build and fill cgroupstats so that taskstats can export it to user * space. * * @stats: cgroupstats to fill information into * @dentry: A dentry entry belonging to the cgroup for which stats have * been requested. */ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry) { int ret = -EINVAL; struct cgroup *cgrp; struct cgroup_iter it; struct task_struct *tsk; /* * Validate dentry by checking the superblock operations */ if (dentry->d_sb->s_op != &cgroup_ops) goto err; ret = 0; cgrp = dentry->d_fsdata; rcu_read_lock(); cgroup_iter_start(cgrp, &it); while ((tsk = cgroup_iter_next(cgrp, &it))) { switch (tsk->state) { case TASK_RUNNING: stats->nr_running++; break; case TASK_INTERRUPTIBLE: stats->nr_sleeping++; break; case TASK_UNINTERRUPTIBLE: stats->nr_uninterruptible++; break; case TASK_STOPPED: stats->nr_stopped++; break; default: if (delayacct_is_task_waiting_on_io(tsk)) stats->nr_io_wait++; break; } } cgroup_iter_end(cgrp, &it); rcu_read_unlock(); err: return ret; } static int cmppid(const void *a, const void *b) { return *(pid_t *)a - *(pid_t *)b; } /* * Convert array 'a' of 'npids' pid_t's to a string of newline separated * decimal pids in 'buf'. Don't write more than 'sz' chars, but return * count 'cnt' of how many chars would be written if buf were large enough. */ static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids) { int cnt = 0; int i; for (i = 0; i < npids; i++) cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]); return cnt; } /* * Handle an open on 'tasks' file. Prepare a buffer listing the * process id's of tasks currently attached to the cgroup being opened. * * Does not require any specific cgroup mutexes, and does not take any. */ static int cgroup_tasks_open(struct inode *unused, struct file *file) { struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent); struct ctr_struct *ctr; pid_t *pidarray; int npids; char c; if (!(file->f_mode & FMODE_READ)) return 0; ctr = kmalloc(sizeof(*ctr), GFP_KERNEL); if (!ctr) goto err0; /* * If cgroup gets more users after we read count, we won't have * enough space - tough. This race is indistinguishable to the * caller from the case that the additional cgroup users didn't * show up until sometime later on. */ npids = cgroup_task_count(cgrp); if (npids) { pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL); if (!pidarray) goto err1; npids = pid_array_load(pidarray, npids, cgrp); sort(pidarray, npids, sizeof(pid_t), cmppid, NULL); /* Call pid_array_to_buf() twice, first just to get bufsz */ ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1; ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL); if (!ctr->buf) goto err2; ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids); kfree(pidarray); } else { ctr->buf = 0; ctr->bufsz = 0; } file->private_data = ctr; return 0; err2: kfree(pidarray); err1: kfree(ctr); err0: return -ENOMEM; } static ssize_t cgroup_tasks_read(struct cgroup *cgrp, struct cftype *cft, struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { struct ctr_struct *ctr = file->private_data; return simple_read_from_buffer(buf, nbytes, ppos, ctr->buf, ctr->bufsz); } static int cgroup_tasks_release(struct inode *unused_inode, struct file *file) { struct ctr_struct *ctr; if (file->f_mode & FMODE_READ) { ctr = file->private_data; kfree(ctr->buf); kfree(ctr); } return 0; } static u64 cgroup_read_notify_on_release(struct cgroup *cgrp, struct cftype *cft) { return notify_on_release(cgrp); } static u64 cgroup_read_releasable(struct cgroup *cgrp, struct cftype *cft) { return test_bit(CGRP_RELEASABLE, &cgrp->flags); } /* * for the common functions, 'private' gives the type of file */ static struct cftype files[] = { { .name = "tasks", .open = cgroup_tasks_open, .read = cgroup_tasks_read, .write = cgroup_common_file_write, .release = cgroup_tasks_release, .private = FILE_TASKLIST, }, { .name = "notify_on_release", .read_uint = cgroup_read_notify_on_release, .write = cgroup_common_file_write, .private = FILE_NOTIFY_ON_RELEASE, }, { .name = "releasable", .read_uint = cgroup_read_releasable, .private = FILE_RELEASABLE, } }; static struct cftype cft_release_agent = { .name = "release_agent", .read = cgroup_common_file_read, .write = cgroup_common_file_write, .private = FILE_RELEASE_AGENT, }; static int cgroup_populate_dir(struct cgroup *cgrp) { int err; struct cgroup_subsys *ss; /* First clear out any existing files */ cgroup_clear_directory(cgrp->dentry); err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files)); if (err < 0) return err; if (cgrp == cgrp->top_cgroup) { if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0) return err; } for_each_subsys(cgrp->root, ss) { if (ss->populate && (err = ss->populate(ss, cgrp)) < 0) return err; } return 0; } static void init_cgroup_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss, struct cgroup *cgrp) { css->cgroup = cgrp; atomic_set(&css->refcnt, 0); css->flags = 0; if (cgrp == dummytop) set_bit(CSS_ROOT, &css->flags); BUG_ON(cgrp->subsys[ss->subsys_id]); cgrp->subsys[ss->subsys_id] = css; } /* * cgroup_create - create a cgroup * parent: cgroup that will be parent of the new cgroup. * name: name of the new cgroup. Will be strcpy'ed. * mode: mode to set on new inode * * Must be called with the mutex on the parent inode held */ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, int mode) { struct cgroup *cgrp; struct cgroupfs_root *root = parent->root; int err = 0; struct cgroup_subsys *ss; struct super_block *sb = root->sb; cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL); if (!cgrp) return -ENOMEM; /* Grab a reference on the superblock so the hierarchy doesn't * get deleted on unmount if there are child cgroups. This * can be done outside cgroup_mutex, since the sb can't * disappear while someone has an open control file on the * fs */ atomic_inc(&sb->s_active); mutex_lock(&cgroup_mutex); cgrp->flags = 0; INIT_LIST_HEAD(&cgrp->sibling); INIT_LIST_HEAD(&cgrp->children); INIT_LIST_HEAD(&cgrp->css_sets); INIT_LIST_HEAD(&cgrp->release_list); cgrp->parent = parent; cgrp->root = parent->root; cgrp->top_cgroup = parent->top_cgroup; for_each_subsys(root, ss) { struct cgroup_subsys_state *css = ss->create(ss, cgrp); if (IS_ERR(css)) { err = PTR_ERR(css); goto err_destroy; } init_cgroup_css(css, ss, cgrp); } list_add(&cgrp->sibling, &cgrp->parent->children); root->number_of_cgroups++; err = cgroup_create_dir(cgrp, dentry, mode); if (err < 0) goto err_remove; /* The cgroup directory was pre-locked for us */ BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex)); err = cgroup_populate_dir(cgrp); /* If err < 0, we have a half-filled directory - oh well ;) */ mutex_unlock(&cgroup_mutex); mutex_unlock(&cgrp->dentry->d_inode->i_mutex); return 0; err_remove: list_del(&cgrp->sibling); root->number_of_cgroups--; err_destroy: for_each_subsys(root, ss) { if (cgrp->subsys[ss->subsys_id]) ss->destroy(ss, cgrp); } mutex_unlock(&cgroup_mutex); /* Release the reference count that we took on the superblock */ deactivate_super(sb); kfree(cgrp); return err; } static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode) { struct cgroup *c_parent = dentry->d_parent->d_fsdata; /* the vfs holds inode->i_mutex already */ return cgroup_create(c_parent, dentry, mode | S_IFDIR); } static inline int cgroup_has_css_refs(struct cgroup *cgrp) { /* Check the reference count on each subsystem. Since we * already established that there are no tasks in the * cgroup, if the css refcount is also 0, then there should * be no outstanding references, so the subsystem is safe to * destroy. We scan across all subsystems rather than using * the per-hierarchy linked list of mounted subsystems since * we can be called via check_for_release() with no * synchronization other than RCU, and the subsystem linked * list isn't RCU-safe */ int i; for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; struct cgroup_subsys_state *css; /* Skip subsystems not in this hierarchy */ if (ss->root != cgrp->root) continue; css = cgrp->subsys[ss->subsys_id]; /* When called from check_for_release() it's possible * that by this point the cgroup has been removed * and the css deleted. But a false-positive doesn't * matter, since it can only happen if the cgroup * has been deleted and hence no longer needs the * release agent to be called anyway. */ if (css && atomic_read(&css->refcnt)) { return 1; } } return 0; } static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry) { struct cgroup *cgrp = dentry->d_fsdata; struct dentry *d; struct cgroup *parent; struct cgroup_subsys *ss; struct super_block *sb; struct cgroupfs_root *root; /* the vfs holds both inode->i_mutex already */ mutex_lock(&cgroup_mutex); if (atomic_read(&cgrp->count) != 0) { mutex_unlock(&cgroup_mutex); return -EBUSY; } if (!list_empty(&cgrp->children)) { mutex_unlock(&cgroup_mutex); return -EBUSY; } parent = cgrp->parent; root = cgrp->root; sb = root->sb; if (cgroup_has_css_refs(cgrp)) { mutex_unlock(&cgroup_mutex); return -EBUSY; } for_each_subsys(root, ss) { if (cgrp->subsys[ss->subsys_id]) ss->destroy(ss, cgrp); } spin_lock(&release_list_lock); set_bit(CGRP_REMOVED, &cgrp->flags); if (!list_empty(&cgrp->release_list)) list_del(&cgrp->release_list); spin_unlock(&release_list_lock); /* delete my sibling from parent->children */ list_del(&cgrp->sibling); spin_lock(&cgrp->dentry->d_lock); d = dget(cgrp->dentry); cgrp->dentry = NULL; spin_unlock(&d->d_lock); cgroup_d_remove_dir(d); dput(d); root->number_of_cgroups--; set_bit(CGRP_RELEASABLE, &parent->flags); check_for_release(parent); mutex_unlock(&cgroup_mutex); /* Drop the active superblock reference that we took when we * created the cgroup */ deactivate_super(sb); return 0; } static void cgroup_init_subsys(struct cgroup_subsys *ss) { struct cgroup_subsys_state *css; struct list_head *l; printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name); /* Create the top cgroup state for this subsystem */ ss->root = &rootnode; css = ss->create(ss, dummytop); /* We don't handle early failures gracefully */ BUG_ON(IS_ERR(css)); init_cgroup_css(css, ss, dummytop); /* Update all cgroup groups to contain a subsys * pointer to this state - since the subsystem is * newly registered, all tasks and hence all cgroup * groups are in the subsystem's top cgroup. */ write_lock(&css_set_lock); l = &init_css_set.list; do { struct css_set *cg = list_entry(l, struct css_set, list); cg->subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id]; l = l->next; } while (l != &init_css_set.list); write_unlock(&css_set_lock); /* If this subsystem requested that it be notified with fork * events, we should send it one now for every process in the * system */ if (ss->fork) { struct task_struct *g, *p; read_lock(&tasklist_lock); do_each_thread(g, p) { ss->fork(ss, p); } while_each_thread(g, p); read_unlock(&tasklist_lock); } need_forkexit_callback |= ss->fork || ss->exit; ss->active = 1; } /** * cgroup_init_early - initialize cgroups at system boot, and * initialize any subsystems that request early init. */ int __init cgroup_init_early(void) { int i; kref_init(&init_css_set.ref); kref_get(&init_css_set.ref); INIT_LIST_HEAD(&init_css_set.list); INIT_LIST_HEAD(&init_css_set.cg_links); INIT_LIST_HEAD(&init_css_set.tasks); css_set_count = 1; init_cgroup_root(&rootnode); list_add(&rootnode.root_list, &roots); root_count = 1; init_task.cgroups = &init_css_set; init_css_set_link.cg = &init_css_set; list_add(&init_css_set_link.cgrp_link_list, &rootnode.top_cgroup.css_sets); list_add(&init_css_set_link.cg_link_list, &init_css_set.cg_links); for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; BUG_ON(!ss->name); BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN); BUG_ON(!ss->create); BUG_ON(!ss->destroy); if (ss->subsys_id != i) { printk(KERN_ERR "cgroup: Subsys %s id == %d\n", ss->name, ss->subsys_id); BUG(); } if (ss->early_init) cgroup_init_subsys(ss); } return 0; } /** * cgroup_init - register cgroup filesystem and /proc file, and * initialize any subsystems that didn't request early init. */ int __init cgroup_init(void) { int err; int i; struct proc_dir_entry *entry; err = bdi_init(&cgroup_backing_dev_info); if (err) return err; for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; if (!ss->early_init) cgroup_init_subsys(ss); } err = register_filesystem(&cgroup_fs_type); if (err < 0) goto out; entry = create_proc_entry("cgroups", 0, NULL); if (entry) entry->proc_fops = &proc_cgroupstats_operations; out: if (err) bdi_destroy(&cgroup_backing_dev_info); return err; } /* * proc_cgroup_show() * - Print task's cgroup paths into seq_file, one line for each hierarchy * - Used for /proc/<pid>/cgroup. * - No need to task_lock(tsk) on this tsk->cgroup reference, as it * doesn't really matter if tsk->cgroup changes after we read it, * and we take cgroup_mutex, keeping attach_task() from changing it * anyway. No need to check that tsk->cgroup != NULL, thanks to * the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks * cgroup to top_cgroup. */ /* TODO: Use a proper seq_file iterator */ static int proc_cgroup_show(struct seq_file *m, void *v) { struct pid *pid; struct task_struct *tsk; char *buf; int retval; struct cgroupfs_root *root; retval = -ENOMEM; buf = kmalloc(PAGE_SIZE, GFP_KERNEL); if (!buf) goto out; retval = -ESRCH; pid = m->private; tsk = get_pid_task(pid, PIDTYPE_PID); if (!tsk) goto out_free; retval = 0; mutex_lock(&cgroup_mutex); for_each_root(root) { struct cgroup_subsys *ss; struct cgroup *cgrp; int subsys_id; int count = 0; /* Skip this hierarchy if it has no active subsystems */ if (!root->actual_subsys_bits) continue; for_each_subsys(root, ss) seq_printf(m, "%s%s", count++ ? "," : "", ss->name); seq_putc(m, ':'); get_first_subsys(&root->top_cgroup, NULL, &subsys_id); cgrp = task_cgroup(tsk, subsys_id); retval = cgroup_path(cgrp, buf, PAGE_SIZE); if (retval < 0) goto out_unlock; seq_puts(m, buf); seq_putc(m, '\n'); } out_unlock: mutex_unlock(&cgroup_mutex); put_task_struct(tsk); out_free: kfree(buf); out: return retval; } static int cgroup_open(struct inode *inode, struct file *file) { struct pid *pid = PROC_I(inode)->pid; return single_open(file, proc_cgroup_show, pid); } struct file_operations proc_cgroup_operations = { .open = cgroup_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; /* Display information about each subsystem and each hierarchy */ static int proc_cgroupstats_show(struct seq_file *m, void *v) { int i; seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\n"); mutex_lock(&cgroup_mutex); for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; seq_printf(m, "%s\t%lu\t%d\n", ss->name, ss->root->subsys_bits, ss->root->number_of_cgroups); } mutex_unlock(&cgroup_mutex); return 0; } static int cgroupstats_open(struct inode *inode, struct file *file) { return single_open(file, proc_cgroupstats_show, 0); } static struct file_operations proc_cgroupstats_operations = { .open = cgroupstats_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; /** * cgroup_fork - attach newly forked task to its parents cgroup. * @tsk: pointer to task_struct of forking parent process. * * Description: A task inherits its parent's cgroup at fork(). * * A pointer to the shared css_set was automatically copied in * fork.c by dup_task_struct(). However, we ignore that copy, since * it was not made under the protection of RCU or cgroup_mutex, so * might no longer be a valid cgroup pointer. attach_task() might * have already changed current->cgroups, allowing the previously * referenced cgroup group to be removed and freed. * * At the point that cgroup_fork() is called, 'current' is the parent * task, and the passed argument 'child' points to the child task. */ void cgroup_fork(struct task_struct *child) { task_lock(current); child->cgroups = current->cgroups; get_css_set(child->cgroups); task_unlock(current); INIT_LIST_HEAD(&child->cg_list); } /** * cgroup_fork_callbacks - called on a new task very soon before * adding it to the tasklist. No need to take any locks since no-one * can be operating on this task */ void cgroup_fork_callbacks(struct task_struct *child) { if (need_forkexit_callback) { int i; for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; if (ss->fork) ss->fork(ss, child); } } } /** * cgroup_post_fork - called on a new task after adding it to the * task list. Adds the task to the list running through its css_set * if necessary. Has to be after the task is visible on the task list * in case we race with the first call to cgroup_iter_start() - to * guarantee that the new task ends up on its list. */ void cgroup_post_fork(struct task_struct *child) { if (use_task_css_set_links) { write_lock(&css_set_lock); if (list_empty(&child->cg_list)) list_add(&child->cg_list, &child->cgroups->tasks); write_unlock(&css_set_lock); } } /** * cgroup_exit - detach cgroup from exiting task * @tsk: pointer to task_struct of exiting process * * Description: Detach cgroup from @tsk and release it. * * Note that cgroups marked notify_on_release force every task in * them to take the global cgroup_mutex mutex when exiting. * This could impact scaling on very large systems. Be reluctant to * use notify_on_release cgroups where very high task exit scaling * is required on large systems. * * the_top_cgroup_hack: * * Set the exiting tasks cgroup to the root cgroup (top_cgroup). * * We call cgroup_exit() while the task is still competent to * handle notify_on_release(), then leave the task attached to the * root cgroup in each hierarchy for the remainder of its exit. * * To do this properly, we would increment the reference count on * top_cgroup, and near the very end of the kernel/exit.c do_exit() * code we would add a second cgroup function call, to drop that * reference. This would just create an unnecessary hot spot on * the top_cgroup reference count, to no avail. * * Normally, holding a reference to a cgroup without bumping its * count is unsafe. The cgroup could go away, or someone could * attach us to a different cgroup, decrementing the count on * the first cgroup that we never incremented. But in this case, * top_cgroup isn't going away, and either task has PF_EXITING set, * which wards off any attach_task() attempts, or task is a failed * fork, never visible to attach_task. * */ void cgroup_exit(struct task_struct *tsk, int run_callbacks) { int i; struct css_set *cg; if (run_callbacks && need_forkexit_callback) { for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { struct cgroup_subsys *ss = subsys[i]; if (ss->exit) ss->exit(ss, tsk); } } /* * Unlink from the css_set task list if necessary. * Optimistically check cg_list before taking * css_set_lock */ if (!list_empty(&tsk->cg_list)) { write_lock(&css_set_lock); if (!list_empty(&tsk->cg_list)) list_del(&tsk->cg_list); write_unlock(&css_set_lock); } /* Reassign the task to the init_css_set. */ task_lock(tsk); cg = tsk->cgroups; tsk->cgroups = &init_css_set; task_unlock(tsk); if (cg) put_css_set_taskexit(cg); } /** * cgroup_clone - duplicate the current cgroup in the hierarchy * that the given subsystem is attached to, and move this task into * the new child */ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys) { struct dentry *dentry; int ret = 0; char nodename[MAX_CGROUP_TYPE_NAMELEN]; struct cgroup *parent, *child; struct inode *inode; struct css_set *cg; struct cgroupfs_root *root; struct cgroup_subsys *ss; /* We shouldn't be called by an unregistered subsystem */ BUG_ON(!subsys->active); /* First figure out what hierarchy and cgroup we're dealing * with, and pin them so we can drop cgroup_mutex */ mutex_lock(&cgroup_mutex); again: root = subsys->root; if (root == &rootnode) { printk(KERN_INFO "Not cloning cgroup for unused subsystem %s\n", subsys->name); mutex_unlock(&cgroup_mutex); return 0; } cg = tsk->cgroups; parent = task_cgroup(tsk, subsys->subsys_id); snprintf(nodename, MAX_CGROUP_TYPE_NAMELEN, "node_%d", tsk->pid); /* Pin the hierarchy */ atomic_inc(&parent->root->sb->s_active); /* Keep the cgroup alive */ get_css_set(cg); mutex_unlock(&cgroup_mutex); /* Now do the VFS work to create a cgroup */ inode = parent->dentry->d_inode; /* Hold the parent directory mutex across this operation to * stop anyone else deleting the new cgroup */ mutex_lock(&inode->i_mutex); dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename)); if (IS_ERR(dentry)) { printk(KERN_INFO "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename, PTR_ERR(dentry)); ret = PTR_ERR(dentry); goto out_release; } /* Create the cgroup directory, which also creates the cgroup */ ret = vfs_mkdir(inode, dentry, S_IFDIR | 0755); child = __d_cgrp(dentry); dput(dentry); if (ret) { printk(KERN_INFO "Failed to create cgroup %s: %d\n", nodename, ret); goto out_release; } if (!child) { printk(KERN_INFO "Couldn't find new cgroup %s\n", nodename); ret = -ENOMEM; goto out_release; } /* The cgroup now exists. Retake cgroup_mutex and check * that we're still in the same state that we thought we * were. */ mutex_lock(&cgroup_mutex); if ((root != subsys->root) || (parent != task_cgroup(tsk, subsys->subsys_id))) { /* Aargh, we raced ... */ mutex_unlock(&inode->i_mutex); put_css_set(cg); deactivate_super(parent->root->sb); /* The cgroup is still accessible in the VFS, but * we're not going to try to rmdir() it at this * point. */ printk(KERN_INFO "Race in cgroup_clone() - leaking cgroup %s\n", nodename); goto again; } /* do any required auto-setup */ for_each_subsys(root, ss) { if (ss->post_clone) ss->post_clone(ss, child); } /* All seems fine. Finish by moving the task into the new cgroup */ ret = attach_task(child, tsk); mutex_unlock(&cgroup_mutex); out_release: mutex_unlock(&inode->i_mutex); mutex_lock(&cgroup_mutex); put_css_set(cg); mutex_unlock(&cgroup_mutex); deactivate_super(parent->root->sb); return ret; } /* * See if "cgrp" is a descendant of the current task's cgroup in * the appropriate hierarchy * * If we are sending in dummytop, then presumably we are creating * the top cgroup in the subsystem. * * Called only by the ns (nsproxy) cgroup. */ int cgroup_is_descendant(const struct cgroup *cgrp) { int ret; struct cgroup *target; int subsys_id; if (cgrp == dummytop) return 1; get_first_subsys(cgrp, NULL, &subsys_id); target = task_cgroup(current, subsys_id); while (cgrp != target && cgrp!= cgrp->top_cgroup) cgrp = cgrp->parent; ret = (cgrp == target); return ret; } static void check_for_release(struct cgroup *cgrp) { /* All of these checks rely on RCU to keep the cgroup * structure alive */ if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count) && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) { /* Control Group is currently removeable. If it's not * already queued for a userspace notification, queue * it now */ int need_schedule_work = 0; spin_lock(&release_list_lock); if (!cgroup_is_removed(cgrp) && list_empty(&cgrp->release_list)) { list_add(&cgrp->release_list, &release_list); need_schedule_work = 1; } spin_unlock(&release_list_lock); if (need_schedule_work) schedule_work(&release_agent_work); } } void __css_put(struct cgroup_subsys_state *css) { struct cgroup *cgrp = css->cgroup; rcu_read_lock(); if (atomic_dec_and_test(&css->refcnt) && notify_on_release(cgrp)) { set_bit(CGRP_RELEASABLE, &cgrp->flags); check_for_release(cgrp); } rcu_read_unlock(); } /* * Notify userspace when a cgroup is released, by running the * configured release agent with the name of the cgroup (path * relative to the root of cgroup file system) as the argument. * * Most likely, this user command will try to rmdir this cgroup. * * This races with the possibility that some other task will be * attached to this cgroup before it is removed, or that some other * user task will 'mkdir' a child cgroup of this cgroup. That's ok. * The presumed 'rmdir' will fail quietly if this cgroup is no longer * unused, and this cgroup will be reprieved from its death sentence, * to continue to serve a useful existence. Next time it's released, * we will get notified again, if it still has 'notify_on_release' set. * * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which * means only wait until the task is successfully execve()'d. The * separate release agent task is forked by call_usermodehelper(), * then control in this thread returns here, without waiting for the * release agent task. We don't bother to wait because the caller of * this routine has no use for the exit status of the release agent * task, so no sense holding our caller up for that. * */ static void cgroup_release_agent(struct work_struct *work) { BUG_ON(work != &release_agent_work); mutex_lock(&cgroup_mutex); spin_lock(&release_list_lock); while (!list_empty(&release_list)) { char *argv[3], *envp[3]; int i; char *pathbuf; struct cgroup *cgrp = list_entry(release_list.next, struct cgroup, release_list); list_del_init(&cgrp->release_list); spin_unlock(&release_list_lock); pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); if (!pathbuf) { spin_lock(&release_list_lock); continue; } if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) { kfree(pathbuf); spin_lock(&release_list_lock); continue; } i = 0; argv[i++] = cgrp->root->release_agent_path; argv[i++] = (char *)pathbuf; argv[i] = NULL; i = 0; /* minimal command environment */ envp[i++] = "HOME=/"; envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin"; envp[i] = NULL; /* Drop the lock while we invoke the usermode helper, * since the exec could involve hitting disk and hence * be a slow process */ mutex_unlock(&cgroup_mutex); call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC); kfree(pathbuf); mutex_lock(&cgroup_mutex); spin_lock(&release_list_lock); } spin_unlock(&release_list_lock); mutex_unlock(&cgroup_mutex); }