fsnotify: srcu to protect read side of inode and vfsmount locks

Currently reading the inode->i_fsnotify_marks or
vfsmount->mnt_fsnotify_marks lists are protected by a spinlock on both the
read and the write side.  This patch protects the read side of those lists
with a new single srcu.

Signed-off-by: Eric Paris <eparis@redhat.com>

4 files changed, 110 insertions, 40 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 4788c866473a..4678b416241e 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -144,14 +144,15 @@ void __fsnotify_flush_ignored_mask(struct inode *inode, void *data, int data_is)
 {
         struct fsnotify_mark *mark;
         struct hlist_node *node;
+        int idx;
+
+        idx = srcu_read_lock(&fsnotify_mark_srcu);
 
         if (!hlist_empty(&inode->i_fsnotify_marks)) {
-                spin_lock(&inode->i_lock);
-                hlist_for_each_entry(mark, node, &inode->i_fsnotify_marks, i.i_list) {
+                hlist_for_each_entry_rcu(mark, node, &inode->i_fsnotify_marks, i.i_list) {
                         if (!(mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
                                 mark->ignored_mask = 0;
                 }
-                spin_unlock(&inode->i_lock);
         }
 
         if (data_is == FSNOTIFY_EVENT_FILE) {
@@ -159,14 +160,14 @@ void __fsnotify_flush_ignored_mask(struct inode *inode, void *data, int data_is)
 
                 mnt = ((struct file *)data)->f_path.mnt;
                 if (mnt && !hlist_empty(&mnt->mnt_fsnotify_marks)) {
-                        spin_lock(&mnt->mnt_root->d_lock);
-                        hlist_for_each_entry(mark, node, &mnt->mnt_fsnotify_marks, m.m_list) {
+                        hlist_for_each_entry_rcu(mark, node, &mnt->mnt_fsnotify_marks, m.m_list) {
                                 if (!(mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
                                         mark->ignored_mask = 0;
                         }
-                        spin_unlock(&mnt->mnt_root->d_lock);
                 }
         }
+
+        srcu_read_unlock(&fsnotify_mark_srcu, idx);
 }
 
 static int send_to_group(struct fsnotify_group *group, struct inode *to_tell,
@@ -208,8 +209,10 @@ static bool needed_by_vfsmount(__u32 test_mask, struct vfsmount *mnt)
 int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
              const unsigned char *file_name, u32 cookie)
 {
+        struct fsnotify_mark *mark;
         struct fsnotify_group *group;
         struct fsnotify_event *event = NULL;
+        struct hlist_node *node;
         struct vfsmount *mnt = NULL;
         int idx, ret = 0;
         /* global tests shouldn't care about events on child only the specific event */
@@ -237,35 +240,47 @@ int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
             !needed_by_vfsmount(test_mask, mnt))
                 return 0;
 
-        /*
-         * SRCU!!  the groups list is very very much read only and the path is
-         * very hot.  The VAST majority of events are not going to need to do
-         * anything other than walk the list so it's crazy to pre-allocate.
-         */
-        idx = srcu_read_lock(&fsnotify_grp_srcu);
+        idx = srcu_read_lock(&fsnotify_mark_srcu);
 
         if (test_mask & to_tell->i_fsnotify_mask) {
-                list_for_each_entry_rcu(group, &fsnotify_inode_groups, inode_group_list) {
-                        if (test_mask & group->mask) {
-                                ret = send_to_group(group, to_tell, NULL, mask, data, data_is,
-                                                    cookie, file_name, &event);
+                hlist_for_each_entry_rcu(mark, node, &to_tell->i_fsnotify_marks, i.i_list) {
+
+                        pr_debug("%s: inode_loop: mark=%p mark->mask=%x mark->ignored_mask=%x\n",
+                                 __func__, mark, mark->mask, mark->ignored_mask);
+
+                        if (test_mask & mark->mask & ~mark->ignored_mask) {
+                                group = mark->group;
+                                if (!group)
+                                        continue;
+                                ret = send_to_group(group, to_tell, NULL, mask,
+                                                    data, data_is, cookie, file_name,
+                                                    &event);
                                 if (ret)
                                         goto out;
                         }
                 }
         }
-        if (needed_by_vfsmount(test_mask, mnt)) {
-                list_for_each_entry_rcu(group, &fsnotify_vfsmount_groups, vfsmount_group_list) {
-                        if (test_mask & group->mask) {
-                                ret = send_to_group(group, to_tell, mnt, mask, data, data_is,
-                                                    cookie, file_name, &event);
+
+        if (mnt && (test_mask & mnt->mnt_fsnotify_mask)) {
+                hlist_for_each_entry_rcu(mark, node, &mnt->mnt_fsnotify_marks, m.m_list) {
+
+                        pr_debug("%s: mnt_loop: mark=%p mark->mask=%x mark->ignored_mask=%x\n",
+                                 __func__, mark, mark->mask, mark->ignored_mask);
+
+                        if (test_mask & mark->mask & ~mark->ignored_mask)  {
+                                group = mark->group;
+                                if (!group)
+                                        continue;
+                                ret = send_to_group(group, to_tell, mnt, mask,
+                                                    data, data_is, cookie, file_name,
+                                                    &event);
                                 if (ret)
                                         goto out;
                         }
                 }
         }
 out:
-        srcu_read_unlock(&fsnotify_grp_srcu, idx);
+        srcu_read_unlock(&fsnotify_mark_srcu, idx);
         /*
          * fsnotify_create_event() took a reference so the event can't be cleaned
          * up while we are still trying to add it to lists, drop that one.
@@ -279,8 +294,14 @@ EXPORT_SYMBOL_GPL(fsnotify);
 
 static __init int fsnotify_init(void)
 {
+        int ret;
+
         BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
 
-        return init_srcu_struct(&fsnotify_grp_srcu);
+        ret = init_srcu_struct(&fsnotify_mark_srcu);
+        if (ret)
+                panic("initializing fsnotify_mark_srcu");
+
+        return 0;
 }
-subsys_initcall(fsnotify_init);
+core_initcall(fsnotify_init);
diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h
index 1be54f6f9e7d..7eed86f942ba 100644
--- a/fs/notify/fsnotify.h
+++ b/fs/notify/fsnotify.h
@@ -6,8 +6,6 @@
 #include <linux/srcu.h>
 #include <linux/types.h>
 
-/* protects reads of fsnotify_groups */
-extern struct srcu_struct fsnotify_grp_srcu;
 /* all groups which receive inode fsnotify events */
 extern struct list_head fsnotify_inode_groups;
 /* all groups which receive vfsmount fsnotify events */
@@ -20,6 +18,9 @@ extern __u32 fsnotify_vfsmount_mask;
 /* destroy all events sitting in this groups notification queue */
 extern void fsnotify_flush_notify(struct fsnotify_group *group);
 
+/* protects reads of inode and vfsmount marks list */
+extern struct srcu_struct fsnotify_mark_srcu;
+
 extern void fsnotify_set_inode_mark_mask_locked(struct fsnotify_mark *fsn_mark,
                                                 __u32 mask);
 /* add a mark to an inode */
diff --git a/fs/notify/group.c b/fs/notify/group.c
index 7ac65ed4735b..48d3a6d6e47a 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -30,8 +30,6 @@
 
 /* protects writes to fsnotify_groups and fsnotify_mask */
 static DEFINE_MUTEX(fsnotify_grp_mutex);
-/* protects reads while running the fsnotify_groups list */
-struct srcu_struct fsnotify_grp_srcu;
 /* all groups registered to receive inode filesystem notifications */
 LIST_HEAD(fsnotify_inode_groups);
 /* all groups registered to receive mount point filesystem notifications */
@@ -50,18 +48,17 @@ void fsnotify_recalc_global_mask(void)
         struct fsnotify_group *group;
         __u32 inode_mask = 0;
         __u32 vfsmount_mask = 0;
-        int idx;
 
-        idx = srcu_read_lock(&fsnotify_grp_srcu);
+        mutex_lock(&fsnotify_grp_mutex);
         list_for_each_entry_rcu(group, &fsnotify_inode_groups, inode_group_list)
                 inode_mask |= group->mask;
         list_for_each_entry_rcu(group, &fsnotify_vfsmount_groups, vfsmount_group_list)
                 vfsmount_mask |= group->mask;
-                
-        srcu_read_unlock(&fsnotify_grp_srcu, idx);
 
         fsnotify_inode_mask = inode_mask;
         fsnotify_vfsmount_mask = vfsmount_mask;
+
+        mutex_unlock(&fsnotify_grp_mutex);
 }
 
 /*
@@ -168,6 +165,8 @@ static void fsnotify_destroy_group(struct fsnotify_group *group)
         /* clear all inode marks for this group */
         fsnotify_clear_marks_by_group(group);
 
+        synchronize_srcu(&fsnotify_mark_srcu);
+
         /* past the point of no return, matches the initial value of 1 */
         if (atomic_dec_and_test(&group->num_marks))
                 fsnotify_final_destroy_group(group);
@@ -216,12 +215,7 @@ void fsnotify_put_group(struct fsnotify_group *group)
          */
         __fsnotify_evict_group(group);
 
-        /*
-         * now it's off the list, so the only thing we might care about is
-         * srcu access....
-         */
         mutex_unlock(&fsnotify_grp_mutex);
-        synchronize_srcu(&fsnotify_grp_srcu);
 
         /* and now it is really dead. _Nothing_ could be seeing it */
         fsnotify_recalc_global_mask();
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 69c5a166930c..41f3990f900b 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -85,10 +85,12 @@
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/kthread.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/srcu.h>
 #include <linux/writeback.h> /* for inode_lock */
 
 #include <asm/atomic.h>
@@ -96,6 +98,11 @@
 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"
 
+struct srcu_struct fsnotify_mark_srcu;
+static DEFINE_SPINLOCK(destroy_lock);
+static LIST_HEAD(destroy_list);
+static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
+
 void fsnotify_get_mark(struct fsnotify_mark *mark)
 {
         atomic_inc(&mark->refcnt);
@@ -144,11 +151,14 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark)
 
         list_del_init(&mark->g_list);
 
-        fsnotify_put_mark(mark); /* for i_list and g_list */
-
         spin_unlock(&group->mark_lock);
         spin_unlock(&mark->lock);
 
+        spin_lock(&destroy_lock);
+        list_add(&mark->destroy_list, &destroy_list);
+        spin_unlock(&destroy_lock);
+        wake_up(&destroy_waitq);
+
         /*
          * Some groups like to know that marks are being freed.  This is a
          * callback to the group function to let it know that this mark
@@ -263,12 +273,17 @@ int fsnotify_add_mark(struct fsnotify_mark *mark,
 err:
         mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
         list_del_init(&mark->g_list);
+        mark->group = NULL;
         atomic_dec(&group->num_marks);
-        fsnotify_put_mark(mark);
 
         spin_unlock(&group->mark_lock);
         spin_unlock(&mark->lock);
 
+        spin_lock(&destroy_lock);
+        list_add(&mark->destroy_list, &destroy_list);
+        spin_unlock(&destroy_lock);
+        wake_up(&destroy_waitq);
+
         return ret;
 }
 
@@ -326,3 +341,42 @@ void fsnotify_init_mark(struct fsnotify_mark *mark,
         atomic_set(&mark->refcnt, 1);
         mark->free_mark = free_mark;
 }
+
+static int fsnotify_mark_destroy(void *ignored)
+{
+        struct fsnotify_mark *mark, *next;
+        LIST_HEAD(private_destroy_list);
+
+        for (;;) {
+                spin_lock(&destroy_lock);
+                list_for_each_entry_safe(mark, next, &destroy_list, destroy_list) {
+                        list_del(&mark->destroy_list);
+                        list_add(&mark->destroy_list, &private_destroy_list);
+                }
+                spin_unlock(&destroy_lock);
+
+                synchronize_srcu(&fsnotify_mark_srcu);
+
+                list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
+                        list_del_init(&mark->destroy_list);
+                        fsnotify_put_mark(mark);
+                }
+
+                wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
+        }
+
+        return 0;
+}
+
+static int __init fsnotify_mark_init(void)
+{
+        struct task_struct *thread;
+
+        thread = kthread_run(fsnotify_mark_destroy, NULL,
+                             "fsnotify_mark");
+        if (IS_ERR(thread))
+                panic("unable to start fsnotify mark destruction thread.");
+
+        return 0;
+}
+device_initcall(fsnotify_mark_init);