Re: Xfs lockdep warning with for-dave-for-4.6 branch

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Cc: xfs@oss.sgi.com
Subject: Re: Xfs lockdep warning with for-dave-for-4.6 branch
Date: Wed, 11 May 2016 22:57:56 -0700	[thread overview]
Message-ID: <20160512055756.GE6648@birch.djwong.org> (raw)
In-Reply-To: <94cea603-2782-1c5a-e2df-42db4459a8ce@cn.fujitsu.com>

On Thu, May 12, 2016 at 01:53:44PM +0800, Qu Wenruo wrote:
> Hi Darrick,
> 
> Thanks for your reflink work for xfs first, that's quite a good and useful
> feature, also helps to debug btrfs problems.
> (Without that, there is no good reference for reflink behavior)
> 
> But when testing your for-dave-for-4.6 branch, even I'm just testing btrfs
> with xfstests, kernel report some strange lockdep from xfs:
> 
> ------
> run fstests generic/175 at 2016-05-12 13:22:06
> BTRFS: device fsid 3d5c9c3b-2d08-4f0b-9663-00a88cd218da devid 1 transid 3
> /dev/sdb6
> BTRFS info (device sdb6): disk space caching is enabled
> BTRFS: has skinny extents
> BTRFS: flagging fs with big metadata feature
> BTRFS: creating UUID tree
> BTRFS: device fsid bb75eb48-4c5f-4b75-a41d-f642d70c7294 devid 1 transid 3
> /dev/sdb6
> BTRFS info (device sdb6): disk space caching is enabled
> BTRFS: has skinny extents
> BTRFS: flagging fs with big metadata feature
> BTRFS: creating UUID tree
> 
> 
> =================================
> [ INFO: inconsistent lock state ]
> 4.5.0-rc2+ #4 Tainted: G           O
> ---------------------------------
> inconsistent {RECLAIM_FS-ON-R} -> {IN-RECLAIM_FS-W} usage.
> kswapd0/543 [HC0[0]:SC0[0]:HE1:SE1] takes:
>  (&xfs_nondir_ilock_class){++++-+}, at: [<ffffffffa00781f7>]
> xfs_ilock+0x177/0x200 [xfs]
> {RECLAIM_FS-ON-R} state was registered at:
>   [<ffffffff8110f369>] mark_held_locks+0x79/0xa0
>   [<ffffffff81113a43>] lockdep_trace_alloc+0xb3/0x100
>   [<ffffffff81224623>] kmem_cache_alloc+0x33/0x230
>   [<ffffffffa008acc1>] kmem_zone_alloc+0x81/0x120 [xfs]
>   [<ffffffffa005456e>] xfs_refcountbt_init_cursor+0x3e/0xa0 [xfs]
>   [<ffffffffa0053455>] __xfs_refcount_find_shared+0x75/0x580 [xfs]
>   [<ffffffffa00539e4>] xfs_refcount_find_shared+0x84/0xb0 [xfs]
>   [<ffffffffa005dcb8>] xfs_getbmap+0x608/0x8c0 [xfs]
>   [<ffffffffa007634b>] xfs_vn_fiemap+0xab/0xc0 [xfs]
>   [<ffffffff81244208>] do_vfs_ioctl+0x498/0x670
>   [<ffffffff81244459>] SyS_ioctl+0x79/0x90
>   [<ffffffff81847cd7>] entry_SYSCALL_64_fastpath+0x12/0x6f
> irq event stamp: 510775
> hardirqs last  enabled at (510775): [<ffffffff812245d0>]
> __slab_alloc+0x50/0x70
> hardirqs last disabled at (510774): [<ffffffff812245ae>]
> __slab_alloc+0x2e/0x70
> softirqs last  enabled at (510506): [<ffffffff810c8ea8>]
> __do_softirq+0x358/0x430
> softirqs last disabled at (510489): [<ffffffff810c911d>] irq_exit+0xad/0xb0
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&xfs_nondir_ilock_class);
>   <Interrupt>
>     lock(&xfs_nondir_ilock_class);
> 
>  *** DEADLOCK ***
> 
> 3 locks held by kswapd0/543:
>  #0:  (shrinker_rwsem){++++..}, at: [<ffffffff811e0b78>]
> shrink_slab.part.63.constprop.79+0x48/0x4e0
>  #1:  (&type->s_umount_key#26){++++++}, at: [<ffffffff81232ffb>]
> trylock_super+0x1b/0x50
>  #2:  (sb_internal){.+.+.?}, at: [<ffffffff812327f4>]
> __sb_start_write+0xb4/0xf0
> 
> stack backtrace:
> CPU: 0 PID: 543 Comm: kswapd0 Tainted: G           O    4.5.0-rc2+ #4
> Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox
> 12/01/2006
>  ffffffff82a34f10 ffff88003aa078d0 ffffffff813a14f9 ffff88003d8551c0
>  ffff88003aa07920 ffffffff8110ec65 0000000000000000 0000000000000001
>  ffff880000000001 000000000000000b 0000000000000008 ffff88003d855aa0
> Call Trace:
>  [<ffffffff813a14f9>] dump_stack+0x4b/0x72
>  [<ffffffff8110ec65>] print_usage_bug+0x215/0x240
>  [<ffffffff8110ee85>] mark_lock+0x1f5/0x660
>  [<ffffffff8110e100>] ? print_shortest_lock_dependencies+0x1a0/0x1a0
>  [<ffffffff811102e0>] __lock_acquire+0xa80/0x1e50
>  [<ffffffff8122474e>] ? kmem_cache_alloc+0x15e/0x230
>  [<ffffffffa008acc1>] ? kmem_zone_alloc+0x81/0x120 [xfs]
>  [<ffffffff811122e8>] lock_acquire+0xd8/0x1e0
>  [<ffffffffa00781f7>] ? xfs_ilock+0x177/0x200 [xfs]
>  [<ffffffffa0083a70>] ? xfs_reflink_cancel_cow_range+0x150/0x300 [xfs]
>  [<ffffffff8110aace>] down_write_nested+0x5e/0xc0
>  [<ffffffffa00781f7>] ? xfs_ilock+0x177/0x200 [xfs]
>  [<ffffffffa00781f7>] xfs_ilock+0x177/0x200 [xfs]
>  [<ffffffffa0083a70>] xfs_reflink_cancel_cow_range+0x150/0x300 [xfs]
>  [<ffffffffa0085bdc>] xfs_fs_evict_inode+0xdc/0x1e0 [xfs]
>  [<ffffffff8124d7d5>] evict+0xc5/0x190
>  [<ffffffff8124d8d9>] dispose_list+0x39/0x60
>  [<ffffffff8124eb2b>] prune_icache_sb+0x4b/0x60
>  [<ffffffff8123317f>] super_cache_scan+0x14f/0x1a0
>  [<ffffffff811e0d19>] shrink_slab.part.63.constprop.79+0x1e9/0x4e0
>  [<ffffffff811e50ee>] shrink_zone+0x15e/0x170
>  [<ffffffff811e5ef1>] kswapd+0x4f1/0xa80
>  [<ffffffff811e5a00>] ? zone_reclaim+0x230/0x230
>  [<ffffffff810e6882>] kthread+0xf2/0x110
>  [<ffffffff810e6790>] ? kthread_create_on_node+0x220/0x220
>  [<ffffffff8184803f>] ret_from_fork+0x3f/0x70
>  [<ffffffff810e6790>] ? kthread_create_on_node+0x220/0x220
> hrtimer: interrupt took 4824925 ns
> 
> BTRFS info (device sdb6): disk space caching is enabled
> BTRFS: has skinny extents
> ------
> 
> The test machine is using normal xfs (without -m reflink=1) as its root.
> As you can see, it's running generic/175 on *BTRFS*, not *XFS*, but still
> lockdep warning from xfs.

That's ... odd.  We shouldn't ever be in the refcountbt code if reflink
isn't enabled.  Welp, I'll have a look in the morning.

--D

> 
> Hopes the output could help you.
> 
> Thanks,
> Qu
> 
> 

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