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Wed, 4 Nov 2026 13:19:17 +0000 (GMT) Received: from [9.123.7.57] (unknown [9.123.7.57]) by smtpav01.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 4 Nov 2026 13:19:17 +0000 (GMT) Message-ID: Date: Wed, 4 Nov 2026 18:49:15 +0530 X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] blk-mq: take quiesce_lock when removing a queue from the tag set To: mt4022@columbia.edu, Jens Axboe Cc: Mohamed Khalfella , Keith Busch , Ming Lei , Bart Van Assche , Christoph Hellwig , Josef Bacik , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, tz2294@columbia.edu, stable@vger.kernel.org References: <20261103-blk-mq-del-quiesce-lock-v1-1-04aa29a481f6@columbia.edu> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20261103-blk-mq-del-quiesce-lock-v1-1-04aa29a481f6@columbia.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: yHopyXxG2KnqN6PjutsKsE1_p2on7WHV X-Proofpoint-Spam-Info: AW1haW4tMjYxMTA0MDA1MiBTYWx0ZWRfXx2fpEmoNN6xp 1qdrW7KCZA7vcH9Zkk1fZy5meBlUD/o9ogSbTIKauInuBzHHoZoleN6GOf4VT0JE+kstOaQOt87 Z9H6JE1fatrYpShmUXyQH99LxP1FRBM= X-Authority-Analysis: v=2.4 cv=LokHWXdc c=1 sm=1 tr=0 ts=6aeb30da cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=FgAr1SJcMogouSPLcIcA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTA0MDA1MiBTYWx0ZWRfX91SMM+KJLtSN krkm9/h6fySwsNIzJkPdki/YeAkmQFb37Hn/m799UenZxx5A7/xaPYTN+9DDJdAnBWcSxN2izw9 67OlIIadb0IUFAcnTu9PJt3RVzGaXiCVVdJZR+WPqOHz+k7j/PP5TiC2+BH9eSB3G8BAXYt3LA8 l0PEp5zs5cw1bA620V3sWqoDaQDAySJKWiwlEoBrdDT3koB4Je3Xpc5pJtxK+xIU+hYdaz6YteE lWVIFYFQRDuMduCKQ9XnqzBiuvh7FkdA44VKMF3YNgflfBSYLoLX6iy+10VLWtNpZmU7NNlP7oz 1fS8pjrSco10GJsdWMdYueuwWKW9ziWCT7megbTtif50uplIKly2sjW1JmjntoW+ylFq+dD/sVy 0xoy7dEyDYBDpanhdDo3ESAZFF5KalsIsxhhlyaqbQGvucRTZvPTTFZsJ+JoCID7h4oGrRqPey4 LIyC94HWm3ZnuQta7zw== X-Proofpoint-GUID: UmIB34rF3dfuLEJNp3TqAXQpd7ra9AZz X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-04_04,2026-11-03_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 clxscore=1011 impostorscore=0 priorityscore=1501 suspectscore=0 phishscore=0 malwarescore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611040052 On 11/4/26 12:34 AM, Mani Tofigh via B4 Relay wrote: > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 5ae22d556540..54ccfc43c27c 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -4354,7 +4354,10 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q) > > lockdep_assert_held(&set->tag_list_lock); > > + /* blk_mq_unquiesce_tagset() runs the hctxs, which are not RCU freed */ > + spin_lock(&set->quiesce_lock); > list_del_rcu(&q->tag_set_list); > + spin_unlock(&set->quiesce_lock); > if (list_is_singular(&set->tag_list)) { > /* just transitioned to unshared */ > set->flags &= ~BLK_MQ_F_TAG_QUEUE_SHARED; Now that set->quiesce_lock serializes both traversal of set->tag_list in blk_mq_[un]quiesce_tagset() as well as modifications in blk_mq_[add|del]_queue_tag_set(), do we still need RCU protection for this list? Assuming there are no other lockless readers of set->tag_list, could we use regular list operations in blk_mq_[add|del]_queue_tag_set() and remove the RCU read-side critical sections from blk_mq_[un]quiesce_tagset()? Thanks, --Nilay