[Gluster-devel] fstat problems when killing with stat prefetch turned on

[Amar Tumballi]

Miklos, Thanks for this patch.

Team will review this, and update you on if this is good fix.

-Amar



On Thu, May 4, 2017 at 6:59 PM, Miklós Fokin <miklos.fokin at appeartv.com>
wrote:

> Sorry, missing lines from the attachment.
>
> On 05/04/2017 03:24 PM, Miklós Fokin wrote:
>
> Hello,
>
> I seem to have discovered what caused half of the problem.
> I did update the bug report with a more detailed description, but the
> short version is that the attached diff solves the issue when we get an
> fstat with a size of 0 after killing a brick (not letting the first update
> to fsync be from an arbiter).
> My question is: should I make a review about it or should further needed
> changes be investigated first?
>
> Best regards,
> Miklós
>
>
> On 04/26/2017 12:58 PM, Miklós Fokin wrote:
>
> Thanks for the response.
> We didn't have the options set that the first two reviews were about.
> The third was about changes to performance.readdir-ahead.
> I turned this feature off today with prefetch being turned on on my
> computer, and the bug still appeared, so I would think that the commit
> would not fix it either.
>
> Best regards,
> Miklós
>
>
> On 04/25/2017 01:26 PM, Raghavendra Gowdappa wrote:
>
> Recently we had worked on some patches to ensure correct stats are
> returned.
>
> https://review.gluster.org/15759
> https://review.gluster.org/15659
> https://review.gluster.org/16419
>
> Referring to these patches and bugs associated with them might give you
> some insight into the nature of the problem. The major culprit was
> interaction between readdir-ahead and stat-prefetch. So, the issue you are
> seeing might be addressed by these patches.
>
> ----- Original Message -----
>
> From: "Miklós Fokin" <miklos.fokin at appeartv.com>
> <miklos.fokin at appeartv.com>
> To: gluster-devel at gluster.org
> Sent: Tuesday, April 25, 2017 3:42:52 PM
> Subject: [Gluster-devel] fstat problems when killing with stat prefetch
> turned on
>
> Hello,
>
> I tried reproducing the problem that Mateusz Slupny was experiencing
> before (stat returning bad st_size value on self-healing) on my own
> computer with only 3 bricks (one being an arbiter) on 3.10.0.
> The result with such a small setup was that the bug appeared both on
> killing and during the self-healing process, but only rarely (once in
> hundreds of tries) and only with performance.stat-prefetch turned on.
> This might be a completely different issue as on the setup Matt was
> using, he could reproduce it with the mentioned option being off, it
> always happened but only during recovery, not after killing.
> I did submit a bug report about this:
> https://bugzilla.redhat.com/show_bug.cgi?id=1444892.
>
> The problem is as Matt wrote is that this causes data corruption if one
> is to use the returned size on writing.
> Could I get some pointers as to what parts of the gluster code I should
> be looking at to figure out what the problem might be?
>
> Thanks in advance,
> Miklós
>
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-- 
Amar Tumballi (amarts)
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