From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: dm: snapshot: I/O error failure in xfstests
	generic/081
Date: Thu, 24 Mar 2016 09:25:21 -0400
Message-ID: <20160324132521.GA2605@redhat.com>
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To: Ming Lei <ming.lei@canonical.com>
Cc: dm-devel@redhat.com, Alasdair Kergon <agk@redhat.com>
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On Thu, Mar 24 2016 at  8:23am -0400,
Ming Lei <ming.lei@canonical.com> wrote:

> Hi,
> 
> When I run xfstests generic/081 over virtio-scsi, loop or virtio-blk,
> the following snapshot error and IO failure is alwasy observed in
> linus v4.5+.

The only snapshot specific changes that went into 4.5+ are:

385277b dm snapshot: fix hung bios when copy error occurs
808e621 dm snapshot: disallow the COW and origin devices from being identical

Neither of which should result in "Unable to allocate exception" due to
-ENOMEM.

But commit 385277b does touch relevant code-paths though so you might
try reverting it and see if your problem goes away.

If that doesn't help then you'll have to do a bisect.

Mike

> [1], dmesg log
> [  374.794520] EXT4-fs (dm-3): mounted filesystem with ordered data
> mode. Opts: (null)
> [  392.894924] device-mapper: snapshots: Invalidating snapshot: Unable
> to allocate exception.
> [  392.904760] EXT4-fs warning (device dm-3): ext4_end_bio:314: I/O
> error -5 writing to inode 12 (offset 4194304 size 1048576 starting
> block 14337)
> [  392.905336] EXT4-fs warning (device dm-3): ext4_end_bio:314: I/O
> error -5 writing to inode 12 (offset 0 size 2097152 starting block
> 10241)
> [  392.905340] Buffer I/O error on device dm-3, logical block 10241
> [  392.905342] Buffer I/O error on device dm-3, logical block 10242
> [  392.905343] Buffer I/O error on device dm-3, logical block 10243
> [  392.905345] Buffer I/O error on device dm-3, logical block 10244
> [  392.905349] Buffer I/O error on device dm-3, logical block 10245
> [  392.905351] Buffer I/O error on device dm-3, logical block 10246
> [  392.905352] Buffer I/O error on device dm-3, logical block 10247
> [  392.905353] Buffer I/O error on device dm-3, logical block 10248
> [  392.905355] Buffer I/O error on device dm-3, logical block 10249
> [  392.905357] Buffer I/O error on device dm-3, logical block 10250
> [  392.906708] EXT4-fs warning (device dm-3): ext4_end_bio:314: I/O
> error -5 writing to inode 12 (offset 0 size 2097152 starting block
> 11265)
> [  392.949341] EXT4-fs warning (device dm-3): ext4_end_bio:314: I/O
> error -5 writing to inode 12 (offset 2097152 size 2097152 starting
> block 12289)
> [  392.956143] EXT4-fs warning (device dm-3): ext4_end_bio:314: I/O
> error -5 writing to inode 12 (offset 2097152 size 2097152 starting
> block 13313)