From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 4DA2718651 for ; Mon, 6 Jan 2025 03:40:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736134842; cv=none; b=f3y/m04TZnt/uJpMRx0rnnqS6nq+AJ/oDDfAnzepboDd4mpgNKebA0HRfz2AFVvdYZGgYRU8Kkt5gZF5ZKXglDluS63UEPvP0G5YL5KdrNLkvffaKnBNDlnNe3wWmEb79PEeWdqRkojxK96vNa1UTpUsFmm10c85l/Z+DVm1Kzs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736134842; c=relaxed/simple; bh=fsy8vuer/mJeg/gWSTuhFbQAdHRzr2fZa7uKrL6OZBc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=a2ZbXg7Ia9WWF5mhPLxBXhblbwWMWgRDUw5B8Hu/BFV3p6fxWNqhYS5Fl8NgtVvOWy2HoB0L29MlZShtEL02gR+YkZgvmD16CaFDBgR0VGI4ImxyYmLml5AXAY5Peet2E7YrxOgHoAbsvsz6V4XSUhpj9breNRSS1sr5S372P6M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Mw0FY8dU; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Mw0FY8dU" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1736134839; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3tOJAnIBDB+fr4CPUuhNDC5lL3nuKPSuWa2qdR59qUo=; b=Mw0FY8dUDXeS/J2ScEUgbh7nIdUajEM8NBk2jCHrytj3YJQecjgQddMt5kGhiU2EcYn3Fq 6yWVupxWl69L6otmjt10qkHG4MQR1L879Cnkk8UDB9r/lvZqIeW9fvOmllUvV0Ikco96O3 UPW1I21t/tHLgLxuAfjP+GvpkORcmvQ= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-30-gfSZ1YnTNVmQ_oYUjhCj_Q-1; Sun, 05 Jan 2025 22:40:36 -0500 X-MC-Unique: gfSZ1YnTNVmQ_oYUjhCj_Q-1 X-Mimecast-MFC-AGG-ID: gfSZ1YnTNVmQ_oYUjhCj_Q Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id F28DA1956088; Mon, 6 Jan 2025 03:40:34 +0000 (UTC) Received: from fedora (unknown [10.72.116.65]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0BBB71956088; Mon, 6 Jan 2025 03:40:27 +0000 (UTC) Date: Mon, 6 Jan 2025 11:40:22 +0800 From: Ming Lei To: Damien Le Moal Cc: Jens Axboe , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, Christoph Hellwig , Keith Busch , Sagi Grimberg , Nilay Shroff Subject: Re: [PATCH 1/3] block: Fix sysfs queue freeze and limits lock order Message-ID: References: <20250104132522.247376-1-dlemoal@kernel.org> <20250104132522.247376-2-dlemoal@kernel.org> 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: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 On Mon, Jan 06, 2025 at 12:35:36PM +0900, Damien Le Moal wrote: > On 1/6/25 12:31 PM, Ming Lei wrote: > > On Sat, Jan 04, 2025 at 10:25:20PM +0900, Damien Le Moal wrote: > >> queue_attr_store() always freezes a device queue before calling the > >> attribute store operation. For attributes that control queue limits, the > >> store operation will also lock the queue limits with a call to > >> queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may > >> need to issue commands to a device to obtain limit values from the > >> hardware with the queue limits locked. This creates a potential ABBA > >> deadlock situation if a user attempts to modify a limit (thus freezing > >> the device queue) while the device driver starts a revalidation of the > >> device queue limits. > >> > >> Avoid such deadlock by introducing the ->store_limit() operation in > >> struct queue_sysfs_entry and use this operation for all attributes that > >> modify the device queue limits through the QUEUE_RW_LIMIT_ENTRY() macro > >> definition. queue_attr_store() is modified to call the ->store_limit() > >> operation (if it is defined) without the device queue frozen. The device > >> queue freeze for attributes defining the ->stor_limit() operation is > >> moved to after the operation completes and is done only around the call > >> to queue_limits_commit_update(). > >> > >> Cc: stable@vger.kernel.org # v6.9+ > >> Signed-off-by: Damien Le Moal > >> --- > >> block/blk-sysfs.c | 123 ++++++++++++++++++++++++---------------------- > >> 1 file changed, 64 insertions(+), 59 deletions(-) > >> > >> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > >> index 767598e719ab..4fc0020c73a5 100644 > >> --- a/block/blk-sysfs.c > >> +++ b/block/blk-sysfs.c > >> @@ -24,6 +24,8 @@ struct queue_sysfs_entry { > >> struct attribute attr; > >> ssize_t (*show)(struct gendisk *disk, char *page); > >> ssize_t (*store)(struct gendisk *disk, const char *page, size_t count); > >> + ssize_t (*store_limit)(struct gendisk *disk, struct queue_limits *lim, > >> + const char *page, size_t count); > > > > As I mentioned in another thread, freezing queue may not be needed in > > ->store(), so let's discuss and confirm if it is needed here first. > > > > https://lore.kernel.org/linux-block/Z3tHozKiUqWr7gjO@fedora/ > > > > Also even though freeze is needed, I'd suggest to move freeze in each > > .store() callback for simplifying & avoiding regression. > > The patch would be simpler, sure. But the code would not be simpler in my > opinion as we will repeat the freeze+limits commit+unfreeze pattern in several > callbacks. That is why I made the change to introduce the new store_limit() > callback to have that pattern in a single place. > > And thinking about it, queue_attr_store() should be better commented to clearly > describes the locking rules. The pattern can be enhanced by one new helper or API. But let's discuss if we really need the pattern first. IMO, freeze isn't needed in ->store(). Thanks, Ming