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 20EEE28935D for ; Thu, 10 Jul 2025 08:03:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752134628; cv=none; b=Dk4nL7RR8VCfXovjFfPRgQs472zHfHMY5JgUMC65uWXjPkahMTRMpaVAKWmbJook46ix8LVVj4qxbMcj7wOWAh52Ub5x6tWue2lUmILw1CT2kAuoFnprcUl5kFhEIsJ0ceIccQ2HNjdfCle81Vxl4miws6dEAD8yPgb39K69wVY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752134628; c=relaxed/simple; bh=tABg9cdrJ9tPFMs99lq2WazD83tr86JLM6QguN57cmA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ki34hoz2yAA5W+sRbz7ual9fcbUnY4cdzUT3tU43xkZfKeEWgaj87zHTFlmQaYnXNvcspn363GjqU4eha9sxU2CUaucqEO4Zrhc+Bi8/O25ANgLvAt5u9QvNcRDtTX1F/ZJofdt6eO8Bwkn1cx/nDVQEuG727wxfVNWkVmyejL0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (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 CE4BC67373; Thu, 10 Jul 2025 10:03:41 +0200 (CEST) Date: Thu, 10 Jul 2025 10:03:41 +0200 From: Christoph Hellwig To: Bart Van Assche Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org Subject: Re: [PATCH 0/3] Fix a deadlock related to modifying queue attributes Message-ID: <20250710080341.GA8622@lst.de> References: <20250702182430.3764163-1-bvanassche@acm.org> <20250703090906.GG4757@lst.de> <918963a5-a349-433a-80a8-6d06c609f20e@acm.org> <20250708095707.GA28737@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 Tue, Jul 08, 2025 at 09:11:41AM -0700, Bart Van Assche wrote: > I will look into modifying the SRP tests in the blktests repository such > that these use bio-based mode instead of request-based mode. Note that this just fixes the test case. The fact that request based dm-multipath keeps active requests and thus an elevated q_usage_counter around still exists then, with effects both to sysfs and other users of queue freezing. > So the question remains what to do about these two regressions: > * The deadlock triggered by modifying a sysfs attribute of a > dm-multipath device configured with "queue_if_no_path" and no paths > (temporarily). That's not a deadlock by the classic definition, but yes, it is hang that should be addressed. > * Slower booting of Linux devices that modify sysfs attributes > synchronously during boot. So which attributes are regularly modified? Note that for read-ahead it should be safe to drop the freeze as unlike the others it is not used for splitting I/O to the limits accepted by the hardware. So we could probably drop the freeze IFF the patch documents that it is safe. But it still won't fix the root cause.