block layer bug with 4.4-rc3+

[Andre Przywara]

Hi Ming,

thanks for the answer!

On 15/12/15 11:54, Ming Lei wrote:
> On Tue, Dec 15, 2015 at 7:05 PM, Andre Przywara <andre.przywara at arm.com> wrote:
>> Hi,
>>
>> I've been experiencing issues with at least 4.4-rc3 (including current
> 
> I'd suggest you to test the latest linus tree first, and at least two
> fix patches
> have been merged for blk-merge issue.  If there is still the issue
> with linus tree,
> I am happy to take a look.

Mmh, as said ("including current HEAD") this happens still with the
latest HEAD from Linus (which is "9f9499ae8e64: Linux 4.4-rc5" for me).
Just tested yesterday.
Is there another branch/tree with block fixes I should test? Is it worth
to try any of the upcoming branches in linux-block.git (for-4.5/core,
maybe?)

Thanks,
Andre.

> Thanks,
> 
>> HEAD) on a Calxeda Midway (4*ARM Cortex-A15 (32-bit), 8GB RAM, SATA
>> spinning disk or SSD).
>> After some disk I/O load (kernel compile with -j6) I see the kernel
>> screaming:
>>
>> [  103.736982] ata1.00: exception Emask 0x0 SAct 0x3ffff0 SErr 0x0
>> action 0x6 frozen
>> [  103.744476] ata1.00: failed command: WRITE FPDMA QUEUED
>> [  103.749707] ata1.00: cmd 61/00:20:48:6b:41/08:00:0a:00:00/40 tag 4
>> ncq 1048576 out
>> [  103.749707]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask
>> 0x4 (timeout)
>> [  103.764659] ata1.00: status: { DRDY }
>> [  103.768321] ata1.00: failed command: WRITE FPDMA QUEUED
>> [  103.773547] ata1.00: cmd 61/98:28:48:73:41/42:00:0a:00:00/40 tag 5
>> ncq 8728576 out
>> [  103.773547]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask
>> 0x4 (timeout)
>> < repeated with increasing tag numbers>
>>
>> This repeats for a while, but then seems to recover later, though I
>> haven't checked if there are more issues and rebooted instead to avoid
>> filesystem damage.
>>
>> While I agree that this looks like a disk error on the first glance, I
>> never saw this before 4.4-rc2, had the very same error on different
>> nodes (with another spinning disk and even an SSD) and I can make it
>> vanish by reverting the commit I identified after bisection:
>>
>> commit 578270bfbd2803dc7b0b03fbc2ac119efbc73195
>> Author: Ming Lei <ming.lei at canonical.com>
>> Date:   Tue Nov 24 10:35:29 2015 +0800
>>
>>     block: fix segment split
>> ...
>> I understand that this fix seems sane, but actually reverting it fixes
>> the issue for me: 4.4-rc5 crashed within some minutes with the above
>> log, 4.4-rc5 with 578270bfbd reverted survived 19 hours of continuous
>> kernel compiles without issues.
>> Looking at the git history of that file I see quite some recent changes
>> there, but it's beyond my understanding of the code to spot the real
>> culprit.
>>
>> Can anyone point me to a change in blk-merge.c I could try to revert to
>> identify the real root cause? I can run tests quickly, though a real
>> positive case would need some hours of runtime to be sure it's fine.
>>
>> Many thanks!
>> Cheers,
>> Andre.
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