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Tue, 3 Nov 2026 05:54:01 +0000 (GMT) Received: from [9.61.129.51] (unknown [9.61.129.51]) by smtpav01.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 3 Nov 2026 05:54:01 +0000 (GMT) Message-ID: <44b0d0e5-b14f-4e6c-8e00-16b4af712b7d@linux.ibm.com> Date: Tue, 3 Nov 2026 11:23:59 +0530 X-Mailing-List: linux-kernel@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 2/2] block: set QUEUE_FLAG_NO_ELV_SWITCH under the read lock in del_gendisk() To: Qiliang Yuan , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, Ming Lei , "Shin'ichiro Kawasaki" , Stuart Hayes References: <20261102-bug-nvme-remove-ns-async-v1-0-61780fee111c@gmail.com> <20261102-bug-nvme-remove-ns-async-v1-2-61780fee111c@gmail.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20261102-bug-nvme-remove-ns-async-v1-2-61780fee111c@gmail.com> 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: E5XXn22rnhrjyfyL8Mm5dXsOJuq6Th9K X-Proofpoint-Spam-Info: AW1haW4tMjYxMTAzMDAyMiBTYWx0ZWRfX1x8+iNoUGrSD fuFoE79zriB0B4e1rBCzuVFdjAhV9LgSTmXDY7Rf4csKZ47a4WxiVd96MgOPTHDInaMyUT51QfY 3+3KoQv7pfoYpex3WFXCrgHGgupmfaM= X-Authority-Analysis: v=2.4 cv=LokHWXdc c=1 sm=1 tr=0 ts=6ae976fe cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=QfggKeMjAAAA:8 a=eLFNBQ4JqrOy5HXTT0cA:9 a=QEXdDO2ut3YA:10 a=KawSF8pKvnAe-OBSxQn-:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTAzMDAyMiBTYWx0ZWRfX7T2GCMMi6pBb 6Pb/oBwUYEc1ie8CZ3WxrCzNnNl+K0kyBm5AqUA7HN0r1sEUY/pAdlYYJ6ncbF7a2ndNddXN70Y s1xiW0Kq+Mh0aRMcr9lQlh/O3yHCXe1Tvi5HmMrtyNXTn+1ZerXDOmRL5On1SR6CiBa3gPihfV1 01rWVlSbTIrKLUzJcbedWAfOLdCVcEFTvqXq8UWiclm4J1qFBew9203/CL/YNkerzYW0CJydKvu siFPJPm/e2g9bKzOoTwT0PdikJY+5YoP1N6InjrbC4QU+fu8vxGauA+7IiIRBoBoe0m9YUwqqu9 f0Iv1Ny8GADi7BdjRGljAB344ghnV21RhcrkYf2QT7JcmB2mRPILUIpBosg9TUqsLUvUoix3+W9 I8BFiJMWwJ0BMNEpMT01Ok9C2EuSLvXiCx6chNYWAmHUFd1Ajrig1iiKlCTX/xDYt/Jau0PUoua IahJoCcf8aQ2ig2O23w== X-Proofpoint-GUID: iymZEAkMF_5fSf0SJ2x8NQHePZXaKuRx 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=2026-11-03_01,2026-11-02_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 clxscore=1015 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-2611030022 On 11/2/26 11:44 AM, Qiliang Yuan wrote: > del_gendisk() takes the tag set's update_nr_hwq_lock for write to set > QUEUE_FLAG_NO_ELV_SWITCH, then for read around __del_gendisk(). The > write lock was there to wait for elevator switches from sysfs, which > held the lock for read when the flag was added. > > When several disks of one tag set are deleted at once, as nvme does for > the namespaces of a controller, each write lock waits for the other > disks to get through __del_gendisk() under the read lock, and the > deletions run one after another. > > Elevator switches from sysfs have taken update_nr_hwq_lock for write > since commit 4ff58d6bc9dd4 ("block: serialize elevator changes for the > same queue using a writer lock"), as updates of nr_hw_queues do. Set the > flag under the read lock instead, which still waits for both and keeps > them out. Currently, there's a patch[1] in-review to change update_nr_hwq_lock from write to read while switching elevator. So the proposal in this patch may not work out if the changes in patch[1] are accepted. I understand your proposed patchset but I'd recommend wait a bit till we settle with the patch[1]. [1] https://lore.kernel.org/all/20261031044141.5569-1-laveeshb@laveeshbansal.com/ Thanks, --Nilay