linux-kernel - Re: [LKP] [xfs] 834ffca6f7e: WARNING: CPU: 3 PID: 23390 at fs/xfs/xfs_file.c:700 xfs_file_dio_aio

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Date:	Fri, 27 Mar 2015 08:22:37 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Huang Ying <ying.huang@...ux.intel.com>
Cc:	Dave Chinner <dchinner@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, LKP ML <lkp@...org>
Subject: Re: [LKP] [xfs] 834ffca6f7e: WARNING: CPU: 3 PID: 23390 at
 fs/xfs/xfs_file.c:700 xfs_file_dio_aio_write+0x27c/0x2e0()

On Thu, Mar 26, 2015 at 02:45:19PM +0800, Huang Ying wrote:
> FYI, we noticed the below changes on
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> commit 834ffca6f7e345a79f6f2e2d131b0dfba8a4b67a ("xfs: don't zero partial page cache pages during O_DIRECT writes")

Doing what test, exactly?


> [  354.728419] XFS (vda): Unmounting Filesystem
> [  355.133977] XFS (vda): Mounting V4 Filesystem
> [  355.174239] XFS (vda): Ending clean mount
> [  362.820417] WARNING: CPU: 3 PID: 23390 at fs/xfs/xfs_file.c:700 xfs_file_dio_aio_write+0x27c/0x2e0()
> [  362.822109] Modules linked in: ipmi_watchdog ipmi_msghandler sg sr_mod cdrom ata_generic pata_acpi cirrus syscopyarea sysfillrect sysimgblt ppdev ttm ata_piix snd_pcm snd_timer drm_kms_helper libata snd microcode drm soundcore pcspkr floppy serio_raw i2c_piix4 parport_pc parport acpi_cpufreq
> [  362.828207] CPU: 3 PID: 23390 Comm: dd Not tainted 4.0.0-rc3-next-20150311 #1
> [  362.829908] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
> [  362.831853]  ffffffff81bb5940 ffff88007d5c3d08 ffffffff818b19e6 ffff880077f901f8
> [  362.833873]  0000000000000000 ffff88007d5c3d48 ffffffff8107294a ffffea00010cc240
> [  362.835646]  ffff8800570f7400 ffff8800570f75d0 0000000000000000 ffff8800570f7720
> [  362.837330] Call Trace:
> [  362.838593]  [<ffffffff818b19e6>] dump_stack+0x4c/0x65
> [  362.840023]  [<ffffffff8107294a>] warn_slowpath_common+0x8a/0xc0
> [  362.841652]  [<ffffffff81072a3a>] warn_slowpath_null+0x1a/0x20
> [  362.843125]  [<ffffffff8134b75c>] xfs_file_dio_aio_write+0x27c/0x2e0
> [  362.844694]  [<ffffffff8134bb20>] xfs_file_write_iter+0x110/0x130
> [  362.846229]  [<ffffffff811e8861>] new_sync_write+0x81/0xb0
> [  362.847670]  [<ffffffff811e9057>] vfs_write+0xb7/0x1f0
> [  362.849152]  [<ffffffff811e9b6e>] ? vfs_read+0x11e/0x140
> [  362.850573]  [<ffffffff811e9c86>] SyS_write+0x46/0xb0
> [  362.852055]  [<ffffffff818b9e50>] system_call_fastpath+0x12/0x17
> [  362.853576] ---[ end trace 002c13cd5d358e1d ]---

That's warning about a failure to invalidate the page cache across
the region of a direct IO which is a potential data corruption
event. The open(2) man page warns that applications should not do
this....

Also the commit you point out as being problematic was introduced in
3.17-rc3 as part of a series to reduce data corruption problems when
mixing concurrent O_DIRECT and buffered/mmap IO to the same file.
That warning was put there on purpose to tell us that there's a
well known reason the user is reporting data corruption....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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