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Date: Mon, 9 Feb 2026 15:57:21 +0100
From: Christoph Hellwig <hch@lst.de>
To: Yu Kuai <yukuai@fnnas.com>
Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
	sven@kernel.org, j@jannau.net, linux-block@vger.kernel.org,
	linux-nvme@lists.infradead.org, tj@kernel.org, nilay@linux.ibm.com,
	ming.lei@redhat.com, neal@gompa.dev, asahi@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/4] nvme-rdma: move blk_mq_update_nr_hw_queues after
 nvme_unfreeze
Message-ID: <20260209145721.GA18315@lst.de>
References: <20260209082953.3053721-1-yukuai@fnnas.com> <20260209082953.3053721-2-yukuai@fnnas.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Feb 09, 2026 at 04:29:50PM +0800, Yu Kuai wrote:
> blk_mq_update_nr_hw_queues() freezes and unfreezes queues internally.
> When the queue is already frozen before this call, the freeze depth
> becomes 2. The internal unfreeze only decrements it to 1, leaving the
> queue still frozen when debugfs_create_files() is called.
> 
> This triggers WARN_ON_ONCE(q->mq_freeze_depth != 0) in
> debugfs_create_files() and risks deadlock.
> 
> Fix this by moving nvme_unfreeze() before blk_mq_update_nr_hw_queues()
> so the queue is unfrozen before the call, allowing the internal
> freeze/unfreeze to work correctly.

After this nothing is really protected by the frozen queue except
for unquiescing the I/O queues.  So we can probably eventually
drop it, but it might make sense to avoid that for now.

Reviewed-by: Christoph Hellwig <hch@lst.de>