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Tue, 25 Feb 2025 07:59:00 +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 XOBUCkR4vWdmdQAAD6G6ig (envelope-from ); Tue, 25 Feb 2025 07:59:00 +0000 Message-ID: <4e1feba0-e4c4-44fa-a6fa-437a927dbd60@suse.de> Date: Tue, 25 Feb 2025 08:58:59 +0100 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv3 7/7] block: protect read_ahead_kb using q->limits_lock To: Nilay Shroff , linux-block@vger.kernel.org Cc: hch@lst.de, ming.lei@redhat.com, dlemoal@kernel.org, axboe@kernel.dk, gjoyce@ibm.com References: <20250224133102.1240146-1-nilay@linux.ibm.com> <20250224133102.1240146-8-nilay@linux.ibm.com> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <20250224133102.1240146-8-nilay@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_SEVEN(0.00)[7]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_DN_SOME(0.00)[] X-Spam-Flag: NO X-Spam-Level: On 2/24/25 14:30, Nilay Shroff wrote: > The bdi->ra_pages could be updated under q->limits_lock because it's > usually calculated from the queue limits by queue_limits_commit_update. > So protect reading/writing the sysfs attribute read_ahead_kb using > q->limits_lock instead of q->sysfs_lock. > > Signed-off-by: Nilay Shroff > --- > block/blk-sysfs.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index 8f47d9f30fbf..228f81a9060f 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -93,9 +93,9 @@ static ssize_t queue_ra_show(struct gendisk *disk, char *page) > { > ssize_t ret; > > - mutex_lock(&disk->queue->sysfs_lock); > + mutex_lock(&disk->queue->limits_lock); > ret = queue_var_show(disk->bdi->ra_pages << (PAGE_SHIFT - 10), page); > - mutex_unlock(&disk->queue->sysfs_lock); > + mutex_unlock(&disk->queue->limits_lock); > > return ret; > } > @@ -111,12 +111,15 @@ queue_ra_store(struct gendisk *disk, const char *page, size_t count) > ret = queue_var_store(&ra_kb, page, count); > if (ret < 0) > return ret; > - > - mutex_lock(&q->sysfs_lock); > + /* > + * ->ra_pages is protected by ->limits_lock because it is usually > + * calculated from the queue limits by queue_limits_commit_update. > + */ > + mutex_lock(&q->limits_lock); > memflags = blk_mq_freeze_queue(q); > disk->bdi->ra_pages = ra_kb >> (PAGE_SHIFT - 10); > + mutex_unlock(&q->limits_lock); > blk_mq_unfreeze_queue(q, memflags); > - mutex_unlock(&q->sysfs_lock); > Cf my comments to the previous patch: Ordering. Here we take the lock _before_ 'freeze', with the previous patch we took the lock _after_ 'freeze'. Why? 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