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Wed, 10 Sep 2025 10:05:56 +0000 (GMT) Message-ID: <66eea7dc-48b9-43b9-ab3c-1c9c8a00fcac@linux.ibm.com> Date: Wed, 10 Sep 2025 15:35:55 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 for-6.18/block 04/10] blk-mq: convert to serialize updating nr_requests with update_nr_hwq_lock To: Yu Kuai , axboe@kernel.dk, ming.lei@redhat.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com References: <20250910080445.239096-1-yukuai1@huaweicloud.com> <20250910080445.239096-5-yukuai1@huaweicloud.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20250910080445.239096-5-yukuai1@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 2vjdUhL-cV-0VOV-JHh23D50pslOfNvm X-Proofpoint-GUID: 2vjdUhL-cV-0VOV-JHh23D50pslOfNvm X-Authority-Analysis: v=2.4 cv=EYDIQOmC c=1 sm=1 tr=0 ts=68c14d8a cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=i0EeH86SAAAA:8 a=VnNF1IyMAAAA:8 a=FnwBxSr36n09Vd6Btt8A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA2MDAyMCBTYWx0ZWRfXzx20bEwcRzy8 sBKePjchIM1Memybdm2rET8y+zk+JF3IpmoyeFbRZc80cw8Z4FF3jTpabVMbnpfriYLzpjKb1f1 a/0k9gnA2biyZxt1DO6yIJAL8VcV2xgYUAh+Z1xzrxTlHV2ePQTYD3qdB1sIvePhPZhYI8/xd8n Xxznyl1S2DFTADfK34xkSHvStrjLqZmk+t3Qz1pBG2DqnSOfY1wMzvaOEPo8QRECaGFjAgehgu7 +dhE1ZNoqmwbh+s+bA2ByZvfPLBgw2sbESKcRc5ZA20aslZ/qLFlN9x/+fbtQuzdSCCL9ccMF35 OxTC/BBprp7anI53VarVf7ReSf7oTSv0cU9DH1s6ekZxPjVXJIB50cj8cej99XDdetiENbiKslH UDNO17KL X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-09_03,2025-09-10_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 suspectscore=0 spamscore=0 impostorscore=0 priorityscore=1501 phishscore=0 clxscore=1015 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509060020 On 9/10/25 1:34 PM, Yu Kuai wrote: > From: Yu Kuai > > request_queue->nr_requests can be changed by: > > a) switch elevator by updating nr_hw_queues > b) switch elevator by elevator sysfs attribute > c) configue queue sysfs attribute nr_requests > > Current lock order is: > > 1) update_nr_hwq_lock, case a,b > 2) freeze_queue > 3) elevator_lock, case a,b,c > > And update nr_requests is seriablized by elevator_lock() already, > however, in the case c, we'll have to allocate new sched_tags if > nr_requests grow, and do this with elevator_lock held and queue > freezed has the risk of deadlock. > > Hence use update_nr_hwq_lock instead, make it possible to allocate > memory if tags grow, meanwhile also prevent nr_requests to be changed > concurrently. > > Signed-off-by: Yu Kuai Looks good to me: Reviewed-by: Nilay Shroff