From: Ming Lei <ming.lei@redhat.com>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: Jens Axboe <axboe@kernel.dk>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [PATCH] blk-mq: fix corruption with direct issue
Date: Fri, 7 Dec 2018 17:30:17 +0800 [thread overview]
Message-ID: <20181207093016.GE29027@ming.t460p> (raw)
In-Reply-To: <20181207034437.GB22188@ming.t460p>
On Fri, Dec 07, 2018 at 11:44:39AM +0800, Ming Lei wrote:
> On Thu, Dec 06, 2018 at 09:46:42PM -0500, Theodore Y. Ts'o wrote:
> > On Wed, Dec 05, 2018 at 11:03:01AM +0800, Ming Lei wrote:
> > >
> > > But at that time, there isn't io scheduler for MQ, so in theory the
> > > issue should be there since v4.11, especially 945ffb60c11d ("mq-deadline:
> > > add blk-mq adaptation of the deadline IO scheduler").
> >
> > Hi Ming,
> >
> > How were serious you about this issue being there (theoretically) an
> > issue since 4.11? Can you talk about how it might get triggered, and
> > how we can test for it? The reason why I ask is because we're trying
> > to track down a mysterious file system corruption problem on a 4.14.x
> > stable kernel. The symptoms are *very* eerily similar to kernel
> > bugzilla #201685.
>
> Hi Theodore,
>
> It is just a theory analysis.
>
> blk_mq_try_issue_directly() is called in two branches of blk_mq_make_request(),
> both are on real MQ disks.
>
> IO merge can be done on none or real io schedulers, so in theory there might
> be the risk from v4.1, but IO merge on sw queue didn't work for a bit long,
> especially it was fixed by ab42f35d9cb5ac49b5a2.
>
> As Jens mentioned in bugzilla, there are several conditions required
> for triggering the issue:
>
> - MQ device
>
> - queue busy can be triggered. It is hard to trigger in NVMe PCI,
> but may be possible on NVMe FC. However, it can be quite easy to
> trigger on SCSI devices. We know there are some MQ SCSI HBA,
> qlogic FC, megaraid_sas.
>
> - IO merge is enabled.
>
> I have setup scsi_debug in the following way:
>
> modprobe scsi_debug dev_size_mb=4096 clustering=1 \
> max_luns=1 submit_queues=2 max_queue=2
>
> - submit_queues=2 may set this disk as MQ
> - max_queue=4 may trigger the queue busy condition easily
>
> and run some write IO on ext4 over the disk: fio, kernel building,... for
> some time, but still can't trigger the data corruption once.
>
> I should have created more LUN, so that queue may be easier to become
> busy, will do that soon.
Actually I should have used SDEBUG_OPT_HOST_BUSY to simulate the queue busy.
Thanks,
Ming
next prev parent reply other threads:[~2018-12-07 9:30 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-04 22:47 [PATCH] blk-mq: fix corruption with direct issue Jens Axboe
2018-12-05 1:37 ` Ming Lei
2018-12-05 2:16 ` Jens Axboe
2018-12-05 2:23 ` Jens Axboe
2018-12-05 2:27 ` Ming Lei
2018-12-05 2:30 ` Jens Axboe
2018-12-05 2:58 ` Ming Lei
2018-12-05 3:03 ` Ming Lei
2018-12-05 3:05 ` Jens Axboe
2018-12-07 2:46 ` Theodore Y. Ts'o
2018-12-07 3:04 ` Jens Axboe
2018-12-07 3:44 ` Ming Lei
2018-12-07 9:30 ` Ming Lei [this message]
2018-12-05 3:04 ` Jens Axboe
2018-12-05 1:38 ` Guenter Roeck
2018-12-05 2:25 ` Jens Axboe
2018-12-05 17:55 ` Guenter Roeck
2018-12-05 17:59 ` Jens Axboe
2018-12-05 19:09 ` Guenter Roeck
2018-12-05 20:11 ` Jens Axboe
2018-12-05 14:41 ` Christoph Hellwig
2018-12-05 15:15 ` Jens Axboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181207093016.GE29027@ming.t460p \
--to=ming.lei@redhat.com \
--cc=axboe@kernel.dk \
--cc=linux-block@vger.kernel.org \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).