From: Tejun Heo <tj@kernel.org>
To: Dennis Zhou <dennisszhou@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>,
Johannes Weiner <hannes@cmpxchg.org>,
Josef Bacik <josef@toxicpanda.com>,
kernel-team@fb.com, linux-block@vger.kernel.org,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/12] blkcg: fix ref count issue with bio_blkcg using task_css
Date: Fri, 7 Sep 2018 09:52:03 -0700 [thread overview]
Message-ID: <20180907165203.GA1100574@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20180906211045.29055-2-dennisszhou@gmail.com>
On Thu, Sep 06, 2018 at 05:10:34PM -0400, Dennis Zhou wrote:
> From: "Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
>
> The accessor function bio_blkcg either returns the blkcg associated with
> the bio or finds one in the current context. This can cause an issue
> when trying to associate a bio with a blkcg. Particularly, it's the
> third case that is problematic:
>
> return css_to_blkcg(task_css(current, io_cgrp_id));
>
> As the above may race against task migration and the cgroup exiting, it
> is not always ok to take a reference on the blkcg returned from
> bio_blkcg.
>
> This patch adds association ahead of calling bio_blkcg rather than
> after. This makes association a required and explicit step along the
> code paths for calling bio_blkcg. blk_get_rl is modified as well to get
> a reference to the blkcg it may use and blk_put_rl will always put the
> reference back. Association is also moved above the bio_blkcg call to
> ensure it will not return NULL in blk-iolatency.
>
> BFQ and CFQ utilize this flaw, but due to the complexity, I do not want
> to address this in this series. I've created a private version of the
> function with notes not to use it describing the flaw. Hopefully soon,
> that code can be cleaned up.
>
> Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
--
tejun
next prev parent reply other threads:[~2018-09-07 16:52 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 21:10 [PATCH 00/12] block: always associate blkg and refcount cleanup Dennis Zhou
2018-09-06 21:10 ` [PATCH 01/12] blkcg: fix ref count issue with bio_blkcg using task_css Dennis Zhou
2018-09-07 16:52 ` Tejun Heo [this message]
2018-09-06 21:10 ` [PATCH 02/12] blkcg: update blkg_lookup_create to do locking Dennis Zhou
2018-09-07 6:17 ` Liu Bo
2018-09-06 21:10 ` [PATCH 03/12] blkcg: convert blkg_lookup_create to find closest blkg Dennis Zhou
2018-09-07 17:27 ` Tejun Heo
2018-09-07 20:33 ` Dennis Zhou
2018-09-06 21:10 ` [PATCH 04/12] blkcg: always associate a bio with a blkg Dennis Zhou
2018-09-06 21:10 ` [PATCH 05/12] blkcg: consolidate bio_issue_init to be a part of core Dennis Zhou
2018-09-07 19:18 ` Liu Bo
2018-09-06 21:10 ` [PATCH 06/12] blkcg: associate a blkg for pages being evicted by swap Dennis Zhou
2018-09-06 21:10 ` [PATCH 07/12] blkcg: associate writeback bios with a blkg Dennis Zhou
2018-09-06 21:10 ` [PATCH 08/12] blkcg: remove bio->bi_css and instead use bio->bi_blkg Dennis Zhou
2018-09-06 21:10 ` [PATCH 09/12] blkcg: remove additional reference to the css Dennis Zhou
2018-09-07 17:54 ` Tejun Heo
2018-09-07 20:24 ` Dennis Zhou
2018-09-06 21:10 ` [PATCH 10/12] blkcg: cleanup and make blk_get_rl use blkg_lookup_create Dennis Zhou
2018-09-11 5:11 ` [LKP] [blkcg] 1d0e59f90b: BUG:unable_to_handle_kernel kernel test robot
2018-09-06 21:10 ` [PATCH 11/12] blkcg: change blkg reference counting to use percpu_ref Dennis Zhou
2018-09-07 17:59 ` Tejun Heo
2018-09-06 21:10 ` [PATCH 12/12] blkcg: rename blkg_try_get to blkg_tryget Dennis Zhou
-- strict thread matches above, loose matches on Subject: below --
2018-09-11 18:41 [PATCH v3 00/12] block: always associate blkg and refcount cleanup Dennis Zhou
2018-09-11 18:41 ` [PATCH 01/12] blkcg: fix ref count issue with bio_blkcg using task_css Dennis Zhou
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