From: Li Zefan <lizf@cn.fujitsu.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: linux kernel mailing list <linux-kernel@vger.kernel.org>,
Jens Axboe <jaxboe@fusionio.com>
Subject: Re: [PATCH] blk-throttle: Use task_subsys_state() to determine a task's blkio_cgroup
Date: Tue, 10 May 2011 11:49:50 +0800 [thread overview]
Message-ID: <4DC8B5DE.1090103@cn.fujitsu.com> (raw)
In-Reply-To: <20110509134915.GC5975@redhat.com>
Vivek Goyal wrote:
> Currentlly we first map the task to cgroup and then cgroup to
> blkio_cgroup. There is a more direct way to get to blkio_cgroup
> from task using task_subsys_state(). Use that.
>
> The real reason for the fix is that it also avoids a race in generic
> cgroup code. During remount/umount rebind_subsystems() is called and
> it can do following with and rcu protection.
>
> cgrp->subsys[i] = NULL;
>
> That means if somebody got hold of cgroup under rcu and then it tried
> to do cgroup->subsys[] to get to blkio_cgroup, it would get NULL which
> is wrong. I was running into this race condition with ltp running on a
> upstream derived kernel and that lead to crash.
>
> So ideally we should also fix cgroup generic code to wait for rcu
> grace period before setting pointer to NULL. Li Zefan is not very keen
> on introducing synchronize_wait() as he thinks it will slow
> down moun/remount/umount operations.
>
> So for the time being atleast fix the kernel crash by taking a more
> direct route to blkio_cgroup.
>
> One tester had reported a crash while running LTP on a derived kernel
> and with this fix crash is no more seen while the test has been
> running for over 6 days.
>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
next prev parent reply other threads:[~2011-05-10 3:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-09 13:49 [PATCH] blk-throttle: Use task_subsys_state() to determine a task's blkio_cgroup Vivek Goyal
2011-05-10 3:49 ` Li Zefan [this message]
2011-05-11 13:12 ` Vivek Goyal
2011-05-16 13:16 ` Vivek Goyal
2011-05-16 13:21 ` 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=4DC8B5DE.1090103@cn.fujitsu.com \
--to=lizf@cn.fujitsu.com \
--cc=jaxboe@fusionio.com \
--cc=linux-kernel@vger.kernel.org \
--cc=vgoyal@redhat.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