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Mon, 2 Nov 2026 07:22:32 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id EnDILjg66GriaAAAD6G6ig (envelope-from ); Mon, 02 Nov 2026 07:22:32 +0000 Message-ID: Date: Mon, 2 Nov 2026 08:22:32 +0100 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 , Nilay Shroff , 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: Hannes Reinecke 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: 8bit X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-11.79 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_TO(0.00)[gmail.com,kernel.org,kernel.dk,lst.de,grimberg.me]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCPT_COUNT_TWELVE(0.00)[12]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[lists.infradead.org,vger.kernel.org,gmail.com,linux.ibm.com,wdc.com]; RCVD_COUNT_TWO(0.00)[2]; TAGGED_RCPT(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email] X-Spam-Score: -11.79 On 11/2/26 7:14 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. > > Disconnect time of an nvme controller that removes its namespaces in > parallel, from a target on the same host, over tcp to 127.0.0.1 and > over nvme-loop, with 4 I/O queues, median of 3 runs on each of two > boots per kernel: > > namespaces transport before after > 8 tcp 85 / 91 ms 51 / 47 ms > 32 tcp 294 / 293 ms 75 / 70 ms > 64 tcp 533 / 550 ms 115 / 124 ms > 64 loop 1283 / 1200 ms 185 / 204 ms > > Signed-off-by: Qiliang Yuan > --- > block/genhd.c | 17 +++++------------ > 1 file changed, 5 insertions(+), 12 deletions(-) > > diff --git a/block/genhd.c b/block/genhd.c > index 10ca8b4d6eea7..5afc60bf139e6 100644 > --- a/block/genhd.c > +++ b/block/genhd.c > @@ -781,16 +781,6 @@ static void __del_gendisk(struct gendisk *disk) > blk_unfreeze_release_lock(q); > } > > -static void disable_elv_switch(struct request_queue *q) > -{ > - struct blk_mq_tag_set *set = q->tag_set; > - WARN_ON_ONCE(!queue_is_mq(q)); > - > - down_write(&set->update_nr_hwq_lock); > - blk_queue_flag_set(QUEUE_FLAG_NO_ELV_SWITCH, q); > - up_write(&set->update_nr_hwq_lock); > -} > - > /** > * del_gendisk - remove the gendisk > * @disk: the struct gendisk to remove > @@ -820,10 +810,13 @@ void del_gendisk(struct gendisk *disk) > } else { > set = disk->queue->tag_set; > > - disable_elv_switch(disk->queue); > - > memflags = memalloc_noio_save(); > down_read(&set->update_nr_hwq_lock); > + /* > + * Set the flag under the read lock, as elevator switches take > + * update_nr_hwq_lock for write. > + */ > + blk_queue_flag_set(QUEUE_FLAG_NO_ELV_SWITCH, disk->queue); > __del_gendisk(disk); > up_read(&set->update_nr_hwq_lock); > memalloc_noio_restore(memflags); > Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich