inotify: use GFP_NOFS under potential memory pressure

inotify can have a watchs removed under filesystem reclaim.

=================================
[ INFO: inconsistent lock state ]
2.6.31-rc2 #16
---------------------------------
inconsistent {IN-RECLAIM_FS-W} -> {RECLAIM_FS-ON-W} usage.
khubd/217 [HC0[0]:SC0[0]:HE1:SE1] takes:
 (iprune_mutex){+.+.?.}, at: [<c10ba899>] invalidate_inodes+0x20/0xe3
{IN-RECLAIM_FS-W} state was registered at:
  [<c10536ab>] __lock_acquire+0x2c9/0xac4
  [<c1053f45>] lock_acquire+0x9f/0xc2
  [<c1308872>] __mutex_lock_common+0x2d/0x323
  [<c1308c00>] mutex_lock_nested+0x2e/0x36
  [<c10ba6ff>] shrink_icache_memory+0x38/0x1b2
  [<c108bfb6>] shrink_slab+0xe2/0x13c
  [<c108c3e1>] kswapd+0x3d1/0x55d
  [<c10449b5>] kthread+0x66/0x6b
  [<c1003fdf>] kernel_thread_helper+0x7/0x10
  [<ffffffff>] 0xffffffff

Two things are needed to fix this.  First we need a method to tell
fsnotify_create_event() to use GFP_NOFS and second we need to stop using
one global IN_IGNORED event and allocate them one at a time.  This solves
current issues with multiple IN_IGNORED on a queue having tail drop
problems and simplifies the allocations since we don't have to worry about
two tasks opperating on the IGNORED event concurrently.

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

4 files changed, 21 insertions, 12 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index ec2f7bd76818..037e878e03fc 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -159,7 +159,9 @@ void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const
                         if (!group->ops->should_send_event(group, to_tell, mask))
                                 continue;
                         if (!event) {
-                                event = fsnotify_create_event(to_tell, mask, data, data_is, file_name, cookie);
+                                event = fsnotify_create_event(to_tell, mask, data,
+                                                              data_is, file_name, cookie,
+                                                              GFP_KERNEL);
                                 /* shit, we OOM'd and now we can't tell, maybe
                                  * someday someone else will want to do something
                                  * here */
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 726118a5845b..f30d9bbc2e1b 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -57,7 +57,6 @@ int inotify_max_user_watches __read_mostly;
 
 static struct kmem_cache *inotify_inode_mark_cachep __read_mostly;
 struct kmem_cache *event_priv_cachep __read_mostly;
-static struct fsnotify_event *inotify_ignored_event;
 
 /*
  * When inotify registers a new group it increments this and uses that
@@ -384,12 +383,19 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry,
                                     struct fsnotify_group *group)
 {
         struct inotify_inode_mark_entry *ientry;
+        struct fsnotify_event *ignored_event;
         struct inotify_event_private_data *event_priv;
         struct fsnotify_event_private_data *fsn_event_priv;
 
+        ignored_event = fsnotify_create_event(NULL, FS_IN_IGNORED, NULL,
+                                              FSNOTIFY_EVENT_NONE, NULL, 0,
+                                              GFP_NOFS);
+        if (!ignored_event)
+                return;
+
         ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);
 
-        event_priv = kmem_cache_alloc(event_priv_cachep, GFP_KERNEL);
+        event_priv = kmem_cache_alloc(event_priv_cachep, GFP_NOFS);
         if (unlikely(!event_priv))
                 goto skip_send_ignore;
 
@@ -398,7 +404,7 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry,
         fsn_event_priv->group = group;
         event_priv->wd = ientry->wd;
 
-        fsnotify_add_notify_event(group, inotify_ignored_event, fsn_event_priv);
+        fsnotify_add_notify_event(group, ignored_event, fsn_event_priv);
 
         /* did the private data get added? */
         if (list_empty(&fsn_event_priv->event_list))
@@ -406,6 +412,9 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry,
 
 skip_send_ignore:
 
+        /* matches the reference taken when the event was created */
+        fsnotify_put_event(ignored_event);
+
         /* remove this entry from the idr */
         inotify_remove_from_idr(group, ientry);
 
@@ -748,9 +757,6 @@ static int __init inotify_user_setup(void)
 
         inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark_entry, SLAB_PANIC);
         event_priv_cachep = KMEM_CACHE(inotify_event_private_data, SLAB_PANIC);
-        inotify_ignored_event = fsnotify_create_event(NULL, FS_IN_IGNORED, NULL, FSNOTIFY_EVENT_NONE, NULL, 0);
-        if (!inotify_ignored_event)
-                panic("unable to allocate the inotify ignored event\n");
 
         inotify_max_queued_events = 16384;
         inotify_max_user_instances = 128;
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 2b20feaf263a..521368574e97 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -153,7 +153,7 @@ static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new
                                 return true;
                         break;
                 case (FSNOTIFY_EVENT_NONE):
-                        return true;
+                        return false;
                 };
         }
         return false;
@@ -345,18 +345,19 @@ static void initialize_event(struct fsnotify_event *event)
  * @name the filename, if available
  */
 struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
-                                             int data_type, const char *name, u32 cookie)
+                                             int data_type, const char *name, u32 cookie,
+                                             gfp_t gfp)
 {
         struct fsnotify_event *event;
 
-        event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
+        event = kmem_cache_alloc(fsnotify_event_cachep, gfp);
         if (!event)
                 return NULL;
 
         initialize_event(event);
 
         if (name) {
-                event->file_name = kstrdup(name, GFP_KERNEL);
+                event->file_name = kstrdup(name, gfp);
                 if (!event->file_name) {
                         kmem_cache_free(fsnotify_event_cachep, event);
                         return NULL;
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 6c3de999fb34..4d6f47b51189 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -352,7 +352,7 @@ extern void fsnotify_unmount_inodes(struct list_head *list);
 /* put here because inotify does some weird stuff when destroying watches */
 extern struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
                                                     void *data, int data_is, const char *name,
-                                                    u32 cookie);
+                                                    u32 cookie, gfp_t gfp);
 
 #else