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authorArjan van de Ven <arjan@linux.intel.com>2006-07-30 03:03:54 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-07-31 13:28:41 -0700
commit5b6509aa8c2f292caea7c0602ec361f920951508 (patch)
tree0edf596a30b5e121c16d1868a0a284eced177f58 /fs/inotify_user.c
parent70ea91f17f7454bc7a285817e883eace2597984f (diff)
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[PATCH] inotify: fix deadlock found by lockdep
This is a real deadlock, a nice complex one: (warning: long explanation follows so that Andrew can have a complete patch description) it's an ABCDA deadlock: A iprune_mutex B inode->inotify_mutex C ih->mutex D dev->ev_mutex The AB relationship comes straight from invalidate_inodes() int invalidate_inodes(struct super_block * sb) { int busy; LIST_HEAD(throw_away); mutex_lock(&iprune_mutex); spin_lock(&inode_lock); inotify_unmount_inodes(&sb->s_inodes); where inotify_umount_inodes() takes the mutex_lock(&inode->inotify_mutex); The BC relationship comes directly from inotify_find_update_watch(): s32 inotify_find_update_watch(struct inotify_handle *ih, struct inode *inode, u32 mask) { ... mutex_lock(&inode->inotify_mutex); mutex_lock(&ih->mutex); The CD relationship comes from inotify_rm_wd: inotify_rm_wd does mutex_lock(&inode->inotify_mutex); mutex_lock(&ih->mutex) and then calls inotify_remove_watch_locked() which calls notify_dev_queue_event() which does mutex_lock(&dev->ev_mutex); (this strictly is a BCD relationship) The DA relationship comes from the most interesting part: [<ffffffff8022d9f2>] shrink_icache_memory+0x42/0x270 [<ffffffff80240dc4>] shrink_slab+0x11d/0x1c9 [<ffffffff802b5104>] try_to_free_pages+0x187/0x244 [<ffffffff8020efed>] __alloc_pages+0x1cd/0x2e0 [<ffffffff8025e1f8>] cache_alloc_refill+0x3f8/0x821 [<ffffffff8020a5e5>] kmem_cache_alloc+0x85/0xcb [<ffffffff802db027>] kernel_event+0x2e/0x122 [<ffffffff8021d61c>] inotify_dev_queue_event+0xcc/0x140 inotify_dev_queue_event schedules a kernel_event which does a kmem_cache_alloc( , GFP_KERNEL) which may try to shrink slabs, including the inode cache .. which then takes iprune_mutex. And voila, there is an AB, a BC, a CD relationship (even a direct BCD), and also now a DA relationship -> a circular type AB-BA deadlock but involving 4 locks. The solution is simple: kernel_event() is NOT allowed to use GFP_KERNEL, but must use GFP_NOFS to not cause recursion into the VFS. Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> Acked-by: Ingo Molnar <mingo@elte.hu> Acked-by: Robert Love <rml@novell.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'fs/inotify_user.c')
-rw-r--r--fs/inotify_user.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/inotify_user.c b/fs/inotify_user.c
index f2386442ade..017cb0f134d 100644
--- a/fs/inotify_user.c
+++ b/fs/inotify_user.c
@@ -187,7 +187,7 @@ static struct inotify_kernel_event * kernel_event(s32 wd, u32 mask, u32 cookie,
{
struct inotify_kernel_event *kevent;
- kevent = kmem_cache_alloc(event_cachep, GFP_KERNEL);
+ kevent = kmem_cache_alloc(event_cachep, GFP_NOFS);
if (unlikely(!kevent))
return NULL;