Re: [locking bug] inotify: inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Mon, 2009-02-16 at 09:13 +0100, Ingo Molnar wrote:

> From 3023a3e27b909b3b309edac4bc9beb8103f127fa Mon Sep 17 00:00:00 2001
> From: Ingo Molnar <mingo@elte.hu>
> Date: Mon, 16 Feb 2009 09:10:32 +0100
> Subject: [PATCH] inotify: fix GFP_KERNEL related deadlock
> 
> enhanced lockdep coverage of __GFP_NOFS turned up this new
> lockdep assert:
> 
> [ 1093.677775]
> [ 1093.677781] =================================
> [ 1093.680031] [ INFO: inconsistent lock state ]
> [ 1093.680031] 2.6.29-rc5-tip-01504-gb49eca1-dirty #1
> [ 1093.680031] ---------------------------------
> [ 1093.680031] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
> [ 1093.680031] kswapd0/308 [HC0[0]:SC0[0]:HE1:SE1] takes:
> [ 1093.680031]  (&inode->inotify_mutex){+.+.?.}, at: [<c0205942>] inotify_inode_is_dead+0x20/0x80
> [ 1093.680031] {RECLAIM_FS-ON-W} state was registered at:
> [ 1093.680031]   [<c01696b9>] mark_held_locks+0x43/0x5b
> [ 1093.680031]   [<c016baa4>] lockdep_trace_alloc+0x6c/0x6e
> [ 1093.680031]   [<c01cf8b0>] kmem_cache_alloc+0x20/0x150
> [ 1093.680031]   [<c040d0ec>] idr_pre_get+0x27/0x6c
> [ 1093.680031]   [<c02056e3>] inotify_handle_get_wd+0x25/0xad
> [ 1093.680031]   [<c0205f43>] inotify_add_watch+0x7a/0x129
> [ 1093.680031]   [<c020679e>] sys_inotify_add_watch+0x20f/0x250
> [ 1093.680031]   [<c010389e>] sysenter_do_call+0x12/0x35
> [ 1093.680031]   [<ffffffff>] 0xffffffff
> [ 1093.680031] irq event stamp: 60417
> [ 1093.680031] hardirqs last  enabled at (60417): [<c018d5f5>] call_rcu+0x53/0x59
> [ 1093.680031] hardirqs last disabled at (60416): [<c018d5b9>] call_rcu+0x17/0x59
> [ 1093.680031] softirqs last  enabled at (59656): [<c0146229>] __do_softirq+0x157/0x16b
> [ 1093.680031] softirqs last disabled at (59651): [<c0106293>] do_softirq+0x74/0x15d
> [ 1093.680031]
> [ 1093.680031] other info that might help us debug this:
> [ 1093.680031] 2 locks held by kswapd0/308:
> [ 1093.680031]  #0:  (shrinker_rwsem){++++..}, at: [<c01b0502>] shrink_slab+0x36/0x189
> [ 1093.680031]  #1:  (&type->s_umount_key#4){+++++.}, at: [<c01e6d77>] shrink_dcache_memory+0x110/0x1fb
> [ 1093.680031]
> [ 1093.680031] stack backtrace:
> [ 1093.680031] Pid: 308, comm: kswapd0 Not tainted 2.6.29-rc5-tip-01504-gb49eca1-dirty #1
> [ 1093.680031] Call Trace:
> [ 1093.680031]  [<c016947a>] valid_state+0x12a/0x13d
> [ 1093.680031]  [<c016954e>] mark_lock+0xc1/0x1e9
> [ 1093.680031]  [<c016a5b4>] ? check_usage_forwards+0x0/0x3f
> [ 1093.680031]  [<c016ab74>] __lock_acquire+0x2c6/0xac8
> [ 1093.680031]  [<c01688d9>] ? register_lock_class+0x17/0x228
> [ 1093.680031]  [<c016b3d3>] lock_acquire+0x5d/0x7a
> [ 1093.680031]  [<c0205942>] ? inotify_inode_is_dead+0x20/0x80
> [ 1093.680031]  [<c08824c4>] __mutex_lock_common+0x3a/0x4cb
> [ 1093.680031]  [<c0205942>] ? inotify_inode_is_dead+0x20/0x80
> [ 1093.680031]  [<c08829ed>] mutex_lock_nested+0x2e/0x36
> [ 1093.680031]  [<c0205942>] ? inotify_inode_is_dead+0x20/0x80
> [ 1093.680031]  [<c0205942>] inotify_inode_is_dead+0x20/0x80
> [ 1093.680031]  [<c01e6672>] dentry_iput+0x90/0xc2
> [ 1093.680031]  [<c01e67a3>] d_kill+0x21/0x45
> [ 1093.680031]  [<c01e6a46>] __shrink_dcache_sb+0x27f/0x355
> [ 1093.680031]  [<c01e6dc5>] shrink_dcache_memory+0x15e/0x1fb
> [ 1093.680031]  [<c01b05ed>] shrink_slab+0x121/0x189
> [ 1093.680031]  [<c01b0d12>] kswapd+0x39f/0x561
> [ 1093.680031]  [<c01ae499>] ? isolate_pages_global+0x0/0x233
> [ 1093.680031]  [<c0157eae>] ? autoremove_wake_function+0x0/0x43
> [ 1093.680031]  [<c01b0973>] ? kswapd+0x0/0x561
> [ 1093.680031]  [<c0157daf>] kthread+0x41/0x82
> [ 1093.680031]  [<c0157d6e>] ? kthread+0x0/0x82
> [ 1093.680031]  [<c01043ab>] kernel_thread_helper+0x7/0x10
> 
> inotify_handle_get_wd() does idr_pre_get() which does a
> kmem_cache_alloc() without __GFP_FS - and is hence deadlockable under
> extreme MM pressure.
> 
> Signed-off-by: Ingo Molnar <mingo@elte.hu>

Looks like a good catch,

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> ---
>  fs/notify/inotify/inotify.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/notify/inotify/inotify.c b/fs/notify/inotify/inotify.c
> index dae3f28..331f2e8 100644
> --- a/fs/notify/inotify/inotify.c
> +++ b/fs/notify/inotify/inotify.c
> @@ -156,7 +156,7 @@ static int inotify_handle_get_wd(struct inotify_handle *ih,
>  	int ret;
>  
>  	do {
> -		if (unlikely(!idr_pre_get(&ih->idr, GFP_KERNEL)))
> +		if (unlikely(!idr_pre_get(&ih->idr, GFP_NOFS)))
>  			return -ENOSPC;
>  		ret = idr_get_new_above(&ih->idr, watch, ih->last_wd+1, &watch->wd);
>  	} while (ret == -EAGAIN);