@@ -61,9 +61,9 @@ static ssize_t blk_mq_hw_sysfs_show(struct kobject *kobj,
if (!entry->show)
return -EIO;
- mutex_lock(&q->sysfs_lock);
+ mutex_lock(&q->elevator_lock);
res = entry->show(hctx, page);
- mutex_unlock(&q->sysfs_lock);
+ mutex_unlock(&q->elevator_lock);
return res;
}
@@ -4094,6 +4094,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
struct blk_mq_ctx *ctx;
struct blk_mq_tag_set *set = q->tag_set;
+ mutex_lock(&q->elevator_lock);
+
queue_for_each_hw_ctx(q, hctx, i) {
cpumask_clear(hctx->cpumask);
hctx->nr_ctx = 0;
@@ -4198,6 +4200,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
hctx->next_cpu = blk_mq_first_mapped_cpu(hctx);
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
}
+
+ mutex_unlock(&q->elevator_lock);
}
/*
@@ -563,12 +563,14 @@ struct request_queue {
struct list_head flush_list;
/*
- * Protects against I/O scheduler switching, particularly when
- * updating q->elevator. Since the elevator update code path may
- * 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.
+ * Protects against I/O scheduler switching, particularly when updating
+ * q->elevator. Since the elevator update code path may also modify q->
+ * nr_requests and wbt latency, this lock also protects the sysfs attrs
+ * nr_requests and wbt_lat_usec. Additionally the nr_hw_queues update may
+ * modify hctx tags, reserved-tags and cpumask, so this lock also helps
+ * protect the hctx attrs.
+ * To ensure proper locking order during an elevator or nr_hw_queue
+ * update, first freeze the queue, then acquire ->elevator_lock.
*/
struct mutex elevator_lock;
Currently, hctx attributes (nr_tags, nr_reserved_tags, and cpu_list) are protected using `q->sysfs_lock`. However, these attributes can be updated in multiple scenarios: - During the driver's probe method. - When updating nr_hw_queues. - When writing to the sysfs attribute nr_requests, which can modify nr_tags. The nr_requests attribute is already protected using q->elevator_lock, but none of the update paths actually use q->sysfs_lock to protect hctx attributes. So to ensure proper synchronization, replace q->sysfs_lock with q->elevator_lock when reading hctx attributes through sysfs. Additionally, blk_mq_update_nr_hw_queues allocates and updates hctx. The allocation of hctx is protected using q->elevator_lock, however, updating hctx params happens without any protection, so safeguard hctx param update path by also using q->elevator_lock. Signed-off-by: Nilay Shroff <nilay@linux.ibm.com> --- Please note that this patch was unit tested against blktests and quick xfstest with lockdep enabled. This patch should go on top of the previous patchset: https://lore.kernel.org/all/20250304102551.2533767-1-nilay@linux.ibm.com/ --- block/blk-mq-sysfs.c | 4 ++-- block/blk-mq.c | 4 ++++ include/linux/blkdev.h | 14 ++++++++------ 3 files changed, 14 insertions(+), 8 deletions(-)