Re: WARNING: CPU: 2 PID: 32343 at fs/btrfs/inode.c:8693 btrfs_destroy_inode+0x278/0x2a0()

Filipe David Manana
2015-03-07T09:35:30Z

On Tue, Mar 3, 2015 at 2:13 PM, Markus Trippelsdorf
<markus@trippelsdorf.de> wrote:
> On 2015.03.02 at 14:29 +0100, Markus Trippelsdorf wrote:
>> On 2015.03.02 at 12:07 +0000, Filipe David Manana wrote:
>> > >> [83159.038708] ------------[ cut here ]------------
>> > >> [83159.038716] WARNING: CPU: 2 PID: 32343 at fs/btrfs/inode.c:8693 btrfs_destroy_inode+0x278/0x2a0()
>> > >> [83159.038718] CPU: 2 PID: 32343 Comm: rm Tainted: G W 4.0.0-rc1-dirty #104
>> > >> [83159.038719] Hardware name: System manufacturer System Product Name/M4A78T-E, BIOS 3503 04/13/2011
>> > >> [83159.038720] 0000000000000000 ffffffff8199990f ffffffff8168d723 0000000000000000
>> > >> [83159.038722] ffffffff8106d2d2 0000000000000000 ffff88005756edf0 ffff880215805800
>> > >> [83159.038723] ffff880169477eb8 ffff88005756edf0 ffffffff8121bab8 ffff880100675000
>> > >> [83159.038725] Call Trace:
>> > >> [83159.038728] [<ffffffff8168d723>] ? dump_stack+0x40/0x50
>> > >> [83159.038731] [<ffffffff8106d2d2>] ? warn_slowpath_common+0x72/0xc0
>> > >> [83159.038732] [<ffffffff8121bab8>] ? btrfs_destroy_inode+0x278/0x2a0
>> > >> [83159.038735] [<ffffffff8111f747>] ? do_unlinkat+0x1a7/0x2e0
>> > >> [83159.038737] [<ffffffff81083974>] ? task_work_run+0xb4/0x100
>> > >> [83159.038740] [<ffffffff8103b9a9>] ? do_notify_resume+0x69/0x80
>> > >> [83159.038742] [<ffffffff81694092>] ? system_call_fastpath+0x12/0x17
>> > >> [83159.038743] ---[ end trace 3b7c45c6e46fe8dd ]---
>> > >> [83159.038744] ------------[ cut here ]------------
>> > >> [83159.038745] WARNING: CPU: 2 PID: 32343 at fs/btrfs/inode.c:8694 btrfs_destroy_inode+0x1f2/0x2a0()
>> > >> [83159.038746] CPU: 2 PID: 32343 Comm: rm Tainted: G W 4.0.0-rc1-dirty #104
>> > >> [83159.038747] Hardware name: System manufacturer System Product Name/M4A78T-E, BIOS 3503 04/13/2011
>> > >> [83159.038747] 0000000000000000 ffffffff8199990f ffffffff8168d723 0000000000000000
>> > >> [83159.038749] ffffffff8106d2d2 0000000000000000 ffff88005756edf0 ffff880215805800
>> > >> [83159.038750] ffff880169477eb8 ffff88005756edf0 ffffffff8121ba32 ffff880100675000
>> > >> [83159.038751] Call Trace:
>> > >> [83159.038753] [<ffffffff8168d723>] ? dump_stack+0x40/0x50
>> > >> [83159.038754] [<ffffffff8106d2d2>] ? warn_slowpath_common+0x72/0xc0
>> > >> [83159.038755] [<ffffffff8121ba32>] ? btrfs_destroy_inode+0x1f2/0x2a0
>> > >> [83159.038757] [<ffffffff8111f747>] ? do_unlinkat+0x1a7/0x2e0
>> > >> [83159.038758] [<ffffffff81083974>] ? task_work_run+0xb4/0x100
>> > >> [83159.038760] [<ffffffff8103b9a9>] ? do_notify_resume+0x69/0x80
>> > >> [83159.038761] [<ffffffff81694092>] ? system_call_fastpath+0x12/0x17
>> > >> [83159.038762] ---[ end trace 3b7c45c6e46fe8de ]---
>> > >
>> > > Unfortunately the issue isn't 100% reproducible, so I unfortunately
>> > > cannot bisect.
>> >
>> > You probably don't need to bisect. The warning is related to the
>> > outstanding_extents counter being != 0:
>> >
>> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/inode.c?id=refs/tags/v4.0-rc1#n8693
>> >
>> > The only change in 4.0 that changes updates to that counter is:
>> >
>> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3e05bde8c3c2dd761da4d52944a087907955a53c
>> >
>> > So that's likely the change you would find with a bisect.
>>
>> OK, thank you. I will revert the commit and see if it fixes the issue.
>
> No. Reverting 3e05bde8c3 does _not_ fix the issue. It still happens.

Ok, so I ran into this as well, and identified the following patch as
the source of the problem:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=dcab6a3b2ae657a2017637083c28ee303b6b1b8e

It's actually very easy to trigger. The following fio job config triggers it:

[global]
ioengine=sync
direct=0
bssplit=130M/100
fallocate=none
filename=foobar

[job1]
numjobs=1
size=1G
rw=randwrite

Then run these steps:

mkfs.btrfs -f /dev/sdd
mount /dev/sdd /mnt
cd /mnt
fio fio_job.ini
cd ..
umount /mnt
(see dmesg)

The important part is that the writes need to be larger than 128Mb.
With btrfs assertions enabled (CONFIG_BTRFS_ASSERT=y) you'll get a
BUG_ON() immediately:

[211158.555563] BTRFS: assertion failed:
BTRFS_I(inode)->outstanding_extents >= num_extents, file:
fs/btrfs/extent-tree.c, line: 4983
[211158.557901] ------------[ cut here ]------------
[211158.558666] kernel BUG at fs/btrfs/ctree.h:4013!
[211158.559660] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
(....)
[211158.561837] Call Trace:
[211158.561837] [<ffffffffa0474666>] drop_outstanding_extent+0x3d/0x6d [btrfs]
[211158.561837] [<ffffffffa047a5b8>]
btrfs_delalloc_release_metadata+0x53/0xfc [btrfs]
(....)

Otherwise only the warnings you reported during inode eviction.

This happens for both direct IO and buffered writes (direct=0). At
least for the direct IO case, the issue happens due to underflows when
decrementing the inode's outstanding_extents counter (after the very
first write we get outstanding_extents = (unsigned)1 - 2 =
4294967295).

thanks

>
> --
> Markus

--
Filipe David Manana,

"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."