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Date: Fri, 16 May 2025 06:51:24 +0200
From: Christoph Hellwig <hch@lst.de>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>, Damien Le Moal <dlemoal@kernel.org>,
	Yu Kuai <yukuai1@huaweicloud.com>, Ming Lei <ming.lei@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/2] block: Fix a deadlock related freezing zoned
 storage devices
Message-ID: <20250516045124.GB12964@lst.de>
References: <20250514202937.2058598-1-bvanassche@acm.org> <20250514202937.2058598-3-bvanassche@acm.org>
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On Wed, May 14, 2025 at 01:29:37PM -0700, Bart Van Assche wrote:
> +/*
> + * Do not call bio_queue_enter() if the BIO_ZONE_WRITE_PLUGGING flag has been
> + * set because this causes blk_mq_freeze_queue() to deadlock if
> + * blk_zone_wplug_bio_work() submits a bio. Calling bio_queue_enter() for bios
> + * on the plug list is not necessary since a q_usage_counter reference is held
> + * while a bio is on the plug list.
> + */

How do we end up with BIO_ZONE_WRITE_PLUGGING set here?  If that flag
was set in a stacking driver we need to clear it before resubmitting
the bio I think.

Can you provide a null_blk based reproducer for your testcase to see
what happens here?

Either way we can't just simply skip taking q_usage_count.