From: Jens Axboe <axboe@kernel.dk>
To: Tejun Heo <tj@kernel.org>
Cc: linux-block@vger.kernel.org, cgroups@vger.kernel.org, bsd@fb.com,
kernel-team@fb.com
Subject: Re: blk-iocost: fix NULL iocg deref from racing against initialization
Date: Tue, 5 Jan 2021 11:33:40 -0700 [thread overview]
Message-ID: <a7723952-93f2-d719-29df-c7e25691cf38@kernel.dk> (raw)
In-Reply-To: <X/Sj014x+U8ubiFT@mtj.duckdns.org>
On 1/5/21 10:37 AM, Tejun Heo wrote:
> When initializing iocost for a queue, its rqos should be registered before
> the blkcg policy is activated to allow policy data initiailization to lookup
> the associated ioc. This unfortunately means that the rqos methods can be
> called on bios before iocgs are attached to all existing blkgs.
>
> While the race is theoretically possible on ioc_rqos_throttle(), it mostly
> happened in ioc_rqos_merge() due to the difference in how they lookup ioc.
> The former determines it from the passed in @rqos and then bails before
> dereferencing iocg if the looked up ioc is disabled, which most likely is
> the case if initialization is still in progress. The latter looked up ioc by
> dereferencing the possibly NULL iocg making it a lot more prone to actually
> triggering the bug.
>
> * Make ioc_rqos_merge() use the same method as ioc_rqos_throttle() to look
> up ioc for consistency.
>
> * Make ioc_rqos_throttle() and ioc_rqos_merge() test for NULL iocg before
> dereferencing it.
Applied, thanks.
--
Jens Axboe
prev parent reply other threads:[~2021-01-05 18:33 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 17:37 blk-iocost: fix NULL iocg deref from racing against initialization Tejun Heo
2021-01-05 18:33 ` Jens Axboe [this message]
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=a7723952-93f2-d719-29df-c7e25691cf38@kernel.dk \
--to=axboe@kernel.dk \
--cc=bsd@fb.com \
--cc=cgroups@vger.kernel.org \
--cc=kernel-team@fb.com \
--cc=linux-block@vger.kernel.org \
--cc=tj@kernel.org \
/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