From: Mike Snitzer <snitzer@redhat.com>
To: Stefan Bader <stefan.bader@canonical.com>
Cc: linux-kernel@vger.kernel.org, dm-devel@redhat.com,
linux-block@vger.kernel.org, Alasdair Kergon <agk@redhat.com>,
Jens Axboe <axboe@kernel.dk>,
Tyler Hicks <tyler.hicks@canonical.com>
Subject: Re: [PATCH 1/1] blk/core: Gracefully handle unset make_request_fn
Date: Thu, 23 Jan 2020 05:35:41 -0500 [thread overview]
Message-ID: <20200123103541.GA28102@redhat.com> (raw)
In-Reply-To: <20200123091713.12623-2-stefan.bader@canonical.com>
On Thu, Jan 23 2020 at 4:17am -0500,
Stefan Bader <stefan.bader@canonical.com> wrote:
> When device-mapper adapted for multi-queue functionality, they
> also re-organized the way the make-request function was set.
> Before, this happened when the device-mapper logical device was
> created. Now it is done once the mapping table gets loaded the
> first time (this also decides whether the block device is request
> or bio based).
>
> However in generic_make_request(), the request function gets used
> without further checks and this happens if one tries to mount such
> a partially set up device.
>
> This can easily be reproduced with the following steps:
> - dmsetup create -n test
> - mount /dev/dm-<#> /mnt
>
> This maybe is something which also should be fixed up in device-
> mapper.
I'll look closer at other options.
> But given there is already a check for an unset queue
> pointer and potentially there could be other drivers which do or
> might do the same, it sounds like a good move to add another check
> to generic_make_request_checks() and to bail out if the request
> function has not been set, yet.
>
> BugLink: https://bugs.launchpad.net/bugs/1860231
From that bug;
"The currently proposed fix introduces no chance of stability
regressions. There is a chance of a very small performance regression
since an additional pointer comparison is performed on each block layer
request but this is unlikely to be noticeable."
This captures my immediate concern: slowing down everyone for this DM
edge-case isn't desirable.
Mike
next prev parent reply other threads:[~2020-01-23 10:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-23 9:17 [PATCH 0/1] Handle NULL make_request_fn in generic_make_request() Stefan Bader
2020-01-23 9:17 ` [PATCH 1/1] blk/core: Gracefully handle unset make_request_fn Stefan Bader
2020-01-23 10:23 ` Tyler Hicks
2020-01-23 10:35 ` Mike Snitzer [this message]
2020-01-23 17:28 ` Mike Snitzer
2020-01-23 18:52 ` Jens Axboe
2020-01-24 6:04 ` Stefan Bader
2020-01-27 19:32 ` Mike Snitzer
2020-01-27 19:39 ` Jens Axboe
2020-01-28 14:32 ` Stefan Bader
2020-01-28 16:26 ` Mike Snitzer
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=20200123103541.GA28102@redhat.com \
--to=snitzer@redhat.com \
--cc=agk@redhat.com \
--cc=axboe@kernel.dk \
--cc=dm-devel@redhat.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=stefan.bader@canonical.com \
--cc=tyler.hicks@canonical.com \
/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).