From: Arjan van de Ven Date: Sun, 30 Jul 2006 10:03:54 +0000 (-0700) Subject: [PATCH] inotify: fix deadlock found by lockdep X-Git-Tag: v2.6.18-rc4~105 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5b6509aa8c2f292caea7c0602ec361f920951508;p=linux-2.6 [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: [] shrink_icache_memory+0x42/0x270 [] shrink_slab+0x11d/0x1c9 [] try_to_free_pages+0x187/0x244 [] __alloc_pages+0x1cd/0x2e0 [] cache_alloc_refill+0x3f8/0x821 [] kmem_cache_alloc+0x85/0xcb [] kernel_event+0x2e/0x122 [] 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 Acked-by: Ingo Molnar Acked-by: Robert Love Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/inotify_user.c b/fs/inotify_user.c index f2386442ad..017cb0f134 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;