pidns: Make the pidns proc mount/umount logic obvious.

Track the number of pids in the proc hash table.  When the number of
pids goes to 0 schedule work to unmount the kernel mount of proc.

Move the mount of proc into alloc_pid when we allocate the pid for
init.

Remove the surprising calls of pid_ns_release proc in fork and
proc_flush_task.  Those code paths really shouldn't know about proc
namespace implementation details and people have demonstrated several
times that finding and understanding those code paths is difficult and
non-obvious.

Because of the call path detach pid is alwasy called with the
rtnl_lock held free_pid is not allowed to sleep, so the work to
unmounting proc is moved to a work queue.  This has the side benefit
of not blocking the entire world waiting for the unnecessary
rcu_barrier in deactivate_locked_super.

In the process of making the code clear and obvious this fixes a bug
reported by Gao feng <gaofeng@cn.fujitsu.com> where we would leak a
mount of proc during clone(CLONE_NEWPID|CLONE_NEWNET) if copy_pid_ns
succeeded and copy_net_ns failed.

Acked-by: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

6 files changed, 26 insertions, 22 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6177fc238fdb..7621dc51cff8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2590,10 +2590,6 @@ void proc_flush_task(struct task_struct *task)
                 proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
                                         tgid->numbers[i].nr);
         }
-
-        upid = &pid->numbers[pid->level];
-        if (upid->nr == 1)
-                pid_ns_release_proc(upid->ns);
 }
 
 static struct dentry *proc_pid_instantiate(struct inode *dir,
diff --git a/fs/proc/root.c b/fs/proc/root.c
index fc1609321a78..f2f251158d35 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -155,11 +155,6 @@ void __init proc_root_init(void)
         err = register_filesystem(&proc_fs_type);
         if (err)
                 return;
-        err = pid_ns_prepare_proc(&init_pid_ns);
-        if (err) {
-                unregister_filesystem(&proc_fs_type);
-                return;
-        }
 
         proc_self_init();
         proc_symlink("mounts", NULL, "self/mounts");
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index c89c9cfcd247..4c96acdb2489 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -21,6 +21,7 @@ struct pid_namespace {
         struct kref kref;
         struct pidmap pidmap[PIDMAP_ENTRIES];
         int last_pid;
+        int nr_hashed;
         struct task_struct *child_reaper;
         struct kmem_cache *pid_cachep;
         unsigned int level;
@@ -32,6 +33,7 @@ struct pid_namespace {
         struct bsd_acct_struct *bacct;
 #endif
         struct user_namespace *user_ns;
+        struct work_struct proc_work;
         kgid_t pid_gid;
         int hide_pid;
         int reboot;     /* group exit code if this pidns was rebooted */
diff --git a/kernel/fork.c b/kernel/fork.c
index 7798c247f4b9..666dc8b06606 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1476,8 +1476,6 @@ bad_fork_cleanup_io:
         if (p->io_context)
                 exit_io_context(p);
 bad_fork_cleanup_namespaces:
-        if (unlikely(clone_flags & CLONE_NEWPID))
-                pid_ns_release_proc(p->nsproxy->pid_ns);
         exit_task_namespaces(p);
 bad_fork_cleanup_mm:
         if (p->mm)
diff --git a/kernel/pid.c b/kernel/pid.c
index 3a5f238c1ca0..e957f8b09136 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -36,6 +36,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/init_task.h>
 #include <linux/syscalls.h>
+#include <linux/proc_fs.h>
 
 #define pid_hashfn(nr, ns)      \
         hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
@@ -270,8 +271,12 @@ void free_pid(struct pid *pid)
         unsigned long flags;
 
         spin_lock_irqsave(&pidmap_lock, flags);
-        for (i = 0; i <= pid->level; i++)
-                hlist_del_rcu(&pid->numbers[i].pid_chain);
+        for (i = 0; i <= pid->level; i++) {
+                struct upid *upid = pid->numbers + i;
+                hlist_del_rcu(&upid->pid_chain);
+                if (--upid->ns->nr_hashed == 0)
+                        schedule_work(&upid->ns->proc_work);
+        }
         spin_unlock_irqrestore(&pidmap_lock, flags);
 
         for (i = 0; i <= pid->level; i++)
@@ -293,6 +298,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
                 goto out;
 
         tmp = ns;
+        pid->level = ns->level;
         for (i = ns->level; i >= 0; i--) {
                 nr = alloc_pidmap(tmp);
                 if (nr < 0)
@@ -303,17 +309,23 @@ struct pid *alloc_pid(struct pid_namespace *ns)
                 tmp = tmp->parent;
         }
 
+        if (unlikely(is_child_reaper(pid))) {
+                if (pid_ns_prepare_proc(ns))
+                        goto out_free;
+        }
+
         get_pid_ns(ns);
-        pid->level = ns->level;
         atomic_set(&pid->count, 1);
         for (type = 0; type < PIDTYPE_MAX; ++type)
                 INIT_HLIST_HEAD(&pid->tasks[type]);
 
         upid = pid->numbers + ns->level;
         spin_lock_irq(&pidmap_lock);
-        for ( ; upid >= pid->numbers; --upid)
+        for ( ; upid >= pid->numbers; --upid) {
                 hlist_add_head_rcu(&upid->pid_chain,
                                 &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
+                upid->ns->nr_hashed++;
+        }
         spin_unlock_irq(&pidmap_lock);
 
 out:
@@ -570,6 +582,7 @@ void __init pidmap_init(void)
         /* Reserve PID 0. We never call free_pidmap(0) */
         set_bit(0, init_pid_ns.pidmap[0].page);
         atomic_dec(&init_pid_ns.pidmap[0].nr_free);
+        init_pid_ns.nr_hashed = 1;
 
         init_pid_ns.pid_cachep = KMEM_CACHE(pid,
                         SLAB_HWCACHE_ALIGN | SLAB_PANIC);
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index b2604950aa50..84591cfeefc1 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -72,6 +72,12 @@ err_alloc:
         return NULL;
 }
 
+static void proc_cleanup_work(struct work_struct *work)
+{
+        struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
+        pid_ns_release_proc(ns);
+}
+
 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
 #define MAX_PID_NS_LEVEL 32
 
@@ -105,6 +111,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
         ns->level = level;
         ns->parent = get_pid_ns(parent_pid_ns);
         ns->user_ns = get_user_ns(user_ns);
+        INIT_WORK(&ns->proc_work, proc_cleanup_work);
 
         set_bit(0, ns->pidmap[0].page);
         atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
@@ -112,15 +119,8 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
         for (i = 1; i < PIDMAP_ENTRIES; i++)
                 atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
 
-        err = pid_ns_prepare_proc(ns);
-        if (err)
-                goto out_put_parent_pid_ns;
-
         return ns;
 
-out_put_parent_pid_ns:
-        put_pid_ns(parent_pid_ns);
-        put_user_ns(user_ns);
 out_free_map:
         kfree(ns->pidmap[0].page);
 out_free: