Messages in this thread Patch in this message | | | From | Nick Piggin <> | Subject | Re: [2.6.27-rc5] inotify_read's ev_mutex vs do_page_fault's mmap_sem... | Date | Wed, 10 Sep 2008 14:07:16 +1000 |
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On Wednesday 10 September 2008 07:03, Daniel J Blueman wrote: > I observed this locking violation [1] while gnome-panel was loading; > this was previously reported at > http://uwsg.iu.edu/hypermail/linux/kernel/0806.3/2881.html . > > Let me know for more information/config/testing. Thanks!
Thanks for the report. I've attached a patch you could test. It compiles (and boots a UML here) but I don't think I've actually tested the inotify path at all, so it may explode on you.
Peter, this copy_*_user stuff is quite a nightmare... Well actually it isn't, if the code is designed with it in mind from the start, but it is easy for people to forget it can take mmap_sem and filesystem locks... Is there a way to annotate it and say "might take mmap_sem for read" for example? So that these LORs will _always_ trigger rather than just once in a million times when the reclaim gods frown on us?
Anyway, Daniel, thanks again...
> Daniel > > --- [1] > > ======================================================= > [ INFO: possible circular locking dependency detected ] > 2.6.27-rc5-233c-debug #2 > ------------------------------------------------------- > gnome-panel/4944 is trying to acquire lock: > (&mm->mmap_sem){----}, at: [<ffffffff806aa40f>] do_page_fault+0x12f/0xae0 > > but task is already holding lock: > (&dev->ev_mutex){--..}, at: [<ffffffff80320ac3>] inotify_read+0xe3/0x200 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #3 (&dev->ev_mutex){--..}: > [<ffffffff80271889>] __lock_acquire+0xd49/0x1190 > [<ffffffff80271d61>] lock_acquire+0x91/0xc0 > [<ffffffff806a5069>] __mutex_lock_common+0xb9/0x430 > [<ffffffff806a54bf>] mutex_lock_nested+0x3f/0x50 > [<ffffffff80321216>] inotify_dev_queue_event+0x46/0x1c0 > [<ffffffff803200e6>] inotify_inode_queue_event+0xc6/0x110 > [<ffffffff802f424c>] fsnotify_create+0x3c/0x70 > [<ffffffff802f4c5d>] vfs_create+0xbd/0xd0 > [<ffffffff802f7dfe>] do_filp_open+0x80e/0x910 > [<ffffffff802e82b0>] do_sys_open+0x80/0x110 > [<ffffffff802e8380>] sys_open+0x20/0x30 > [<ffffffff8020c86b>] system_call_fastpath+0x16/0x1b > [<ffffffffffffffff>] 0xffffffffffffffff > > -> #2 (&ih->mutex){--..}: > [<ffffffff80271889>] __lock_acquire+0xd49/0x1190 > [<ffffffff80271d61>] lock_acquire+0x91/0xc0 > [<ffffffff806a5069>] __mutex_lock_common+0xb9/0x430 > [<ffffffff806a54bf>] mutex_lock_nested+0x3f/0x50 > [<ffffffff8031fe73>] inotify_find_update_watch+0x53/0xe0 > [<ffffffff80320d85>] sys_inotify_add_watch+0x115/0x1d0 > [<ffffffff8020c86b>] system_call_fastpath+0x16/0x1b > [<ffffffffffffffff>] 0xffffffffffffffff > > -> #1 (&inode->inotify_mutex){--..}: > [<ffffffff80271889>] __lock_acquire+0xd49/0x1190 > [<ffffffff80271d61>] lock_acquire+0x91/0xc0 > [<ffffffff806a5069>] __mutex_lock_common+0xb9/0x430 > [<ffffffff806a54bf>] mutex_lock_nested+0x3f/0x50 > [<ffffffff80320070>] inotify_inode_queue_event+0x50/0x110 > [<ffffffff803206e1>] inotify_dentry_parent_queue_event+0x91/0xb0 > [<ffffffff802ebb7f>] __fput+0x7f/0x1f0 > [<ffffffff802ebd15>] fput+0x25/0x30 > [<ffffffff802c84ff>] remove_vma+0x4f/0x90 > [<ffffffff802ca359>] do_munmap+0x2e9/0x330 > [<ffffffff802ca3f5>] sys_munmap+0x55/0x80 > [<ffffffff8020c86b>] system_call_fastpath+0x16/0x1b > [<ffffffffffffffff>] 0xffffffffffffffff > > -> #0 (&mm->mmap_sem){----}: > [<ffffffff80271950>] __lock_acquire+0xe10/0x1190 > [<ffffffff80271d61>] lock_acquire+0x91/0xc0 > [<ffffffff806a56eb>] down_read+0x4b/0x80 > [<ffffffff806aa40f>] do_page_fault+0x12f/0xae0 > [<ffffffff806a7bdd>] error_exit+0x0/0xa9 > [<ffffffff802eac08>] vfs_read+0xc8/0x170 > [<ffffffff802eadb5>] sys_read+0x55/0x90 > [<ffffffff8020c86b>] system_call_fastpath+0x16/0x1b > [<ffffffffffffffff>] 0xffffffffffffffff > > other info that might help us debug this: > > 1 lock held by gnome-panel/4944: > #0: (&dev->ev_mutex){--..}, at: [<ffffffff80320ac3>] > inotify_read+0xe3/0x200 > > stack backtrace: > Pid: 4944, comm: gnome-panel Not tainted 2.6.27-rc5-233c-debug #2 > > Call Trace: > [<ffffffff8026f807>] print_circular_bug_tail+0xa7/0xf0 > [<ffffffff80271950>] __lock_acquire+0xe10/0x1190 > [<ffffffff80271d61>] lock_acquire+0x91/0xc0 > [<ffffffff806aa40f>] ? do_page_fault+0x12f/0xae0 > [<ffffffff806a56eb>] down_read+0x4b/0x80 > [<ffffffff806aa40f>] ? do_page_fault+0x12f/0xae0 > [<ffffffff8025c51a>] ? search_exception_tables+0x2a/0x50 > [<ffffffff806aa40f>] do_page_fault+0x12f/0xae0 > [<ffffffff8026d951>] ? trace_hardirqs_off_caller+0x21/0xc0 > [<ffffffff80213fc0>] ? native_sched_clock+0x90/0xb0 > [<ffffffff80270e39>] ? __lock_acquire+0x2f9/0x1190 > [<ffffffff80270606>] ? mark_held_locks+0x56/0xa0 > [<ffffffff802708bd>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff80270849>] ? trace_hardirqs_on_caller+0x149/0x1b0 > [<ffffffff806a7bdd>] error_exit+0x0/0xa9 > [<ffffffff80459acd>] ? copy_user_generic_string+0x2d/0x40 > [<ffffffff80320b5d>] ? inotify_read+0x17d/0x200 > [<ffffffff8025ee00>] ? autoremove_wake_function+0x0/0x40 > [<ffffffff802708bd>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff802eac08>] vfs_read+0xc8/0x170 > [<ffffffff802eadb5>] sys_read+0x55/0x90 > [<ffffffff8020c86b>] system_call_fastpath+0x16/0x1b Fix inotify lock order reversal with mmap_sem due to holding locks over copy_to_user.
Signed-off-by: Nick Piggin <npiggin@suse.de> --- Index: linux-2.6/fs/inotify_user.c =================================================================== --- linux-2.6.orig/fs/inotify_user.c +++ linux-2.6/fs/inotify_user.c @@ -323,7 +323,7 @@ out: } /* - * remove_kevent - cleans up and ultimately frees the given kevent + * remove_kevent - cleans up the given kevent * * Caller must hold dev->ev_mutex. */ @@ -334,7 +334,13 @@ static void remove_kevent(struct inotify dev->event_count--; dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len; +} +/* + * free_kevent - frees the given kevent. + */ +static void free_kevent(struct inotify_kernel_event *kevent) +{ kfree(kevent->name); kmem_cache_free(event_cachep, kevent); } @@ -350,6 +356,7 @@ static void inotify_dev_event_dequeue(st struct inotify_kernel_event *kevent; kevent = inotify_dev_get_event(dev); remove_kevent(dev, kevent); + free_kevent(kevent); } } @@ -433,17 +440,15 @@ static ssize_t inotify_read(struct file dev = file->private_data; while (1) { - int events; prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE); mutex_lock(&dev->ev_mutex); - events = !list_empty(&dev->events); - mutex_unlock(&dev->ev_mutex); - if (events) { + if (!list_empty(&dev->events)) { ret = 0; - break; + goto have_events; } + mutex_unlock(&dev->ev_mutex); if (file->f_flags & O_NONBLOCK) { ret = -EAGAIN; @@ -459,10 +464,9 @@ static ssize_t inotify_read(struct file } finish_wait(&dev->wq, &wait); - if (ret) - return ret; + return ret; - mutex_lock(&dev->ev_mutex); +have_events: while (1) { struct inotify_kernel_event *kevent; @@ -481,6 +485,13 @@ static ssize_t inotify_read(struct file } break; } + remove_kevent(dev, kevent); + + /* + * Must perform the copy_to_user outside the mutex in order + * to avoid a lock order reversal with mmap_sem. + */ + mutex_unlock(&dev->ev_mutex); if (copy_to_user(buf, &kevent->event, event_size)) { ret = -EFAULT; @@ -498,7 +509,9 @@ static ssize_t inotify_read(struct file count -= kevent->event.len; } - remove_kevent(dev, kevent); + free_kevent(kevent); + + mutex_lock(&dev->ev_mutex); } mutex_unlock(&dev->ev_mutex); | |