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From: Bart Van Assche <bvanassche@acm.org>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, Hannes Reinecke <hare@suse.de>,
	John Garry <john.garry@huawei.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 0/5] blk-mq: fix use-after-free on stale request
Date: Thu, 20 Aug 2020 13:30:38 -0700	[thread overview]
Message-ID: <accb98d8-8186-2e74-a5c3-e0f09ce2b3ff@acm.org> (raw)
In-Reply-To: <20200820180335.3109216-1-ming.lei@redhat.com>

On 8/20/20 11:03 AM, Ming Lei wrote:
> We can't run allocating driver tag and updating tags->rqs[tag] atomically,
> so stale request may be retrieved from tags->rqs[tag]. More seriously, the
> stale request may have been freed via updating nr_requests or switching
> elevator or other use cases.
> 
> It is one long-term issue, and Jianchao previous worked towards using
> static_rqs[] for iterating request, one problem is that it can be hard
> to use when iterating over tagset.
> 
> This patchset takes another different approach for fixing the issue: cache
> freed rqs pages and release them until all tags->rqs[] references on these
> pages are gone.

Hi Ming,

Is this the only possible solution? Would it e.g. be possible to protect the
code that iterates over all tags with rcu_read_lock() / rcu_read_unlock() and
to free pages that contain request pointers only after an RCU grace period has
expired? Would that perhaps result in a simpler solution?

Thanks,

Bart.

  parent reply	other threads:[~2020-08-20 20:30 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-20 18:03 [PATCH 0/5] blk-mq: fix use-after-free on stale request Ming Lei
2020-08-20 18:03 ` [PATCH 1/5] blk-mq: define max_order for allocating rqs pages as macro Ming Lei
2020-08-20 18:03 ` [PATCH 2/5] blk-mq: add helper of blk_mq_get_hw_queue_node Ming Lei
2020-08-25  8:55   ` John Garry
2020-08-20 18:03 ` [PATCH 3/5] blk-mq: add helpers for allocating/freeing pages of request pool Ming Lei
2020-08-20 18:03 ` [PATCH 4/5] blk-mq: cache freed request pool pages Ming Lei
2020-08-20 18:03 ` [PATCH 5/5] blk-mq: check and shrink freed request pool page Ming Lei
2020-08-20 20:30 ` Bart Van Assche [this message]
2020-08-21  2:49   ` [PATCH 0/5] blk-mq: fix use-after-free on stale request Ming Lei
2020-08-26 12:03     ` John Garry
2020-08-26 12:24       ` Ming Lei
2020-08-26 12:34         ` Ming Lei
2020-08-26 12:56           ` John Garry

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