linux-kernel - [PATCH -next 0/4] blk-cgroup: synchronize del_gendisk() with configuring cgroup policy

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Date:   Sat, 17 Dec 2022 11:09:04 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     tj@...nel.org, hch@...radead.org, josef@...icpanda.com,
        axboe@...nel.dk
Cc:     cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com,
        yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [PATCH -next 0/4] blk-cgroup: synchronize del_gendisk() with configuring cgroup policy

From: Yu Kuai <yukuai3@...wei.com>

iocost is initialized when it's configured the first time, and iocost
initializing can race with del_gendisk(), which will cause null pointer
dereference:

t1				t2
ioc_qos_write
 blk_iocost_init
  rq_qos_add
  				del_gendisk
  				 rq_qos_exit
  				 //iocost is removed from q->roqs
  blkcg_activate_policy
   pd_init_fn
    ioc_pd_init
     ioc = q_to_ioc(blkg->q)
     //can't find iocost and return null

And iolatency is about to switch to the same lazy initialization.

This patchset fix this problem by synchronize rq_qos_add() and
blkcg_activate_policy() with rq_qos_exit().

Yu Kuai (4):
  block/rq_qos: protect 'q->rq_qos' with queue_lock in rq_qos_exit()
  block/rq_qos: fail rq_qos_add() after del_gendisk()
  blk-cgroup: add a new interface blkcg_conf_close_bdev()
  blk-cgroup: synchronize del_gendisk() with configuring cgroup policy

 block/blk-cgroup.c     | 12 ++++++++++--
 block/blk-cgroup.h     |  1 +
 block/blk-iocost.c     |  8 ++++----
 block/blk-rq-qos.c     | 25 ++++++++++++++++++++-----
 block/blk-rq-qos.h     | 17 +++++++++++++----
 include/linux/blkdev.h |  1 +
 6 files changed, 49 insertions(+), 15 deletions(-)

-- 
2.31.1