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From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH 6/5] kyber: avoid q->disk dereferences in trace points
Date: Thu, 14 Oct 2021 20:57:02 +0800	[thread overview]
Message-ID: <YWgpHlO8UJ+IY3lB@T590> (raw)
In-Reply-To: <20211012093301.GA27795@lst.de>

Hello Christoph,

On Tue, Oct 12, 2021 at 11:33:01AM +0200, Christoph Hellwig wrote:
> 
> q->disk becomes invalid after the gendisk is removed.  Work around this
> by caching the dev_t for the tracepoints.  The real fix would be to
> properly tear down the I/O schedulers with the gendisk, but that is
> a much more invasive change.

Except for kyber, blkcg code refers q->disk too.

Such as blkg_dev_name() used in showing blk cgroup files, see
tg_print_limit(), but blkcg_exit_queue() is called in queue's release
handler, so q->disk can be referred when reading blkcg file of cgroup
fs from userspace after deleting gendisk.

I think it is fine to move blkcg_exit_queue() into del_gendisk(), but
bfq_exit_queue() is still run from queue's release handler, and bfq's
blkcg policy is deactivated there. That said the referring in reading
bfq's cgroup file still can come after deleting disk, especially kernel
panic could be caused when q->disk is cleared between the check and
calling to bdi_dev_name() in blkg_dev_name().


Thanks,
Ming


  reply	other threads:[~2021-10-14 12:57 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29  7:12 tear down file system I/O in del_gendisk v3 Christoph Hellwig
2021-09-29  7:12 ` [PATCH 1/5] block: call submit_bio_checks under q_usage_counter Christoph Hellwig
2021-10-17  1:14   ` Jens Axboe
2021-09-29  7:12 ` [PATCH 2/5] block: factor out a blk_try_enter_queue helper Christoph Hellwig
2021-09-29  7:12 ` [PATCH 3/5] block: split bio_queue_enter from blk_queue_enter Christoph Hellwig
2021-09-29  7:12 ` [PATCH 4/5] block: drain file system I/O on del_gendisk Christoph Hellwig
2021-09-29  8:17   ` Ming Lei
2021-10-01  4:13     ` Christoph Hellwig
2021-10-05  2:15       ` Ming Lei
2021-09-29  7:12 ` [PATCH 5/5] block: keep q_usage_counter in atomic mode after del_gendisk Christoph Hellwig
2021-10-12  9:33 ` [PATCH 6/5] kyber: avoid q->disk dereferences in trace points Christoph Hellwig
2021-10-14 12:57   ` Ming Lei [this message]
2021-10-14  9:23 ` tear down file system I/O in del_gendisk v3 Yi Zhang
2021-10-17  1:14 ` Jens Axboe

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