From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87BDCF4F7 for ; Fri, 12 Jan 2024 05:46:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id BC33468CFE; Fri, 12 Jan 2024 06:46:36 +0100 (CET) Date: Fri, 12 Jan 2024 06:46:36 +0100 From: Christoph Hellwig To: Ming Lei Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org Subject: Re: [PATCH 2/2] blk-mq: ensure a q_usage_counter reference is held when splitting bios Message-ID: <20240112054636.GB6829@lst.de> References: <20240111135705.2155518-1-hch@lst.de> <20240111135705.2155518-3-hch@lst.de> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) On Fri, Jan 12, 2024 at 06:22:59AM +0800, Ming Lei wrote: > On Thu, Jan 11, 2024 at 02:57:05PM +0100, Christoph Hellwig wrote: > > q_usage_counter is the only thing preventing us from the limits changing > > under us in __bio_split_to_limits, but blk_mq_submit_bio doesn't hold it. > > Can you share why the limits change matters wrt. split? If queue is > live, both new and old one are supposed to work, such as, we don't > freeze queue when changing `max_sectors_kb` via sysfs. Hardware reconfigurations for example, which can happen in nvme for just about every limit, in SCSI for limits controller by the ULD, and in quite a few places for disabling write zeroes or discard.