block: protect read_ahead_kb using q->limits_lock

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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250304102551.2533767-8-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 223da196a548c88f30808b91455f38a5a0fec328..d584461a1d84f0b5c198848a8e9ccb8b8eef4de9 100644 (file)
--- 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);
 
        return ret;
 }
@@ -670,7 +673,8 @@ static struct attribute *queue_attrs[] = {
        &queue_dma_alignment_entry.attr,
 
        /*
-        * Attributes which are protected with q->sysfs_lock.
+        * Attributes which require some form of locking other than
+        * q->sysfs_lock.
         */
        &queue_ra_entry.attr,
 

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0ee3b5c9388eb0c9a4e4ff403dba768846ee57e2..3bee1b4858b6f42802c3d94628bc46d6eb78caf5 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -571,6 +571,9 @@ struct request_queue {
        struct mutex            elevator_lock;
 
        struct mutex            sysfs_lock;
+       /*
+        * Protects queue limits and also sysfs attribute read_ahead_kb.
+        */
        struct mutex            limits_lock;
 
        /*