block: protect wbt_lat_usec using q->elevator_lock

The wbt latency and state could be updated while initializing the
elevator or exiting the elevator. It could be also updated while
configuring IO latency QoS parameters using cgroup. The elevator
code path is now protected with q->elevator_lock. So we should
protect the access to sysfs attribute wbt_lat_usec using q->elevator
_lock instead of q->sysfs_lock. White we're at it, also protect
ioc_qos_write(), which configures wbt parameters via cgroup, using
q->elevator_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/20250304102551.2533767-7-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 6be46e28459be93617b5d4302b2837fa56a4f06b..38e7bf3c3b4f352d4694b36f132ff97078b0b7b7 100644 (file)
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -3248,6 +3248,7 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
        }
 
        memflags = blk_mq_freeze_queue(disk->queue);
+       mutex_lock(&disk->queue->elevator_lock);
        blk_mq_quiesce_queue(disk->queue);
 
        spin_lock_irq(&ioc->lock);
@@ -3355,6 +3356,7 @@ einval:
        spin_unlock_irq(&ioc->lock);
 
        blk_mq_unquiesce_queue(disk->queue);
+       mutex_unlock(&disk->queue->elevator_lock);
        blk_mq_unfreeze_queue(disk->queue, memflags);
 
        ret = -EINVAL;

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index f1fa57de29edeb45a0516a3b241ca26c8e6de1f7..223da196a548c88f30808b91455f38a5a0fec328 100644 (file)
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -557,7 +557,7 @@ static ssize_t queue_wb_lat_show(struct gendisk *disk, char *page)
        ssize_t ret;
        struct request_queue *q = disk->queue;
 
-       mutex_lock(&q->sysfs_lock);
+       mutex_lock(&q->elevator_lock);
        if (!wbt_rq_qos(q)) {
                ret = -EINVAL;
                goto out;
@@ -570,7 +570,7 @@ static ssize_t queue_wb_lat_show(struct gendisk *disk, char *page)
 
        ret = sysfs_emit(page, "%llu\n", div_u64(wbt_get_min_lat(q), 1000));
 out:
-       mutex_unlock(&q->sysfs_lock);
+       mutex_unlock(&q->elevator_lock);
        return ret;
 }
 
@@ -589,8 +589,8 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page,
        if (val < -1)
                return -EINVAL;
 
-       mutex_lock(&q->sysfs_lock);
        memflags = blk_mq_freeze_queue(q);
+       mutex_lock(&q->elevator_lock);
 
        rqos = wbt_rq_qos(q);
        if (!rqos) {
@@ -619,8 +619,8 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page,
 
        blk_mq_unquiesce_queue(q);
 out:
+       mutex_unlock(&q->elevator_lock);
        blk_mq_unfreeze_queue(q, memflags);
-       mutex_unlock(&q->sysfs_lock);
 
        return ret;
 }
@@ -689,19 +689,15 @@ static struct attribute *queue_attrs[] = {
 
 /* Request-based queue attributes that are not relevant for bio-based queues. */
 static struct attribute *blk_mq_queue_attrs[] = {
-       /*
-        * Attributes which are protected with q->sysfs_lock.
-        */
-#ifdef CONFIG_BLK_WBT
-       &queue_wb_lat_entry.attr,
-#endif
        /*
         * Attributes which require some form of locking other than
         * q->sysfs_lock.
         */
        &elv_iosched_entry.attr,
        &queue_requests_entry.attr,
-
+#ifdef CONFIG_BLK_WBT
+       &queue_wb_lat_entry.attr,
+#endif
        /*
         * Attributes which don't require locking.
         */
@@ -882,10 +878,10 @@ int blk_register_queue(struct gendisk *disk)
                        goto out_crypto_sysfs_unregister;
                }
        }
+       wbt_enable_default(disk);
        mutex_unlock(&q->elevator_lock);
 
        blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);
-       wbt_enable_default(disk);
 
        /* Now everything is ready and send out KOBJ_ADD uevent */
        kobject_uevent(&disk->queue_kobj, KOBJ_ADD);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 3e66ad016a230fb39111a369f2a0f467a73a500f..0ee3b5c9388eb0c9a4e4ff403dba768846ee57e2 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -563,8 +563,8 @@ struct request_queue {
        /*
         * Protects against I/O scheduler switching, particularly when
         * updating q->elevator. Since the elevator update code path may
-        * also modify q->nr_requests, this lock also protects the sysfs
-        * attribute nr_requests.
+        * also modify q->nr_requests and wbt latency, this lock also
+        * protects the sysfs attributes nr_requests and wbt_lat_usec.
         * To ensure proper locking order during an elevator update, first
         * freeze the queue, then acquire ->elevator_lock.
         */