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-rw-r--r--block/blk-mq-sysfs.c6
-rw-r--r--block/blk-mq.c18
-rw-r--r--block/blk-sysfs.c11
3 files changed, 22 insertions, 13 deletions
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index ed5217867555..371d8800b48a 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -402,6 +402,12 @@ static void blk_mq_sysfs_init(struct request_queue *q)
}
}
+/* see blk_register_queue() */
+void blk_mq_finish_init(struct request_queue *q)
+{
+ percpu_ref_switch_to_percpu(&q->mq_usage_counter);
+}
+
int blk_mq_register_disk(struct gendisk *disk)
{
struct device *dev = disk_to_dev(disk);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index df8e1e09dd17..38f4a165640d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -119,16 +119,7 @@ void blk_mq_freeze_queue(struct request_queue *q)
spin_unlock_irq(q->queue_lock);
if (freeze) {
- /*
- * XXX: Temporary kludge to work around SCSI blk-mq stall.
- * SCSI synchronously creates and destroys many queues
- * back-to-back during probe leading to lengthy stalls.
- * This will be fixed by keeping ->mq_usage_counter in
- * atomic mode until genhd registration, but, for now,
- * let's work around using expedited synchronization.
- */
- __percpu_ref_kill_expedited(&q->mq_usage_counter);
-
+ percpu_ref_kill(&q->mq_usage_counter);
blk_mq_run_queues(q, false);
}
wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
@@ -1804,7 +1795,12 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
if (!q)
goto err_hctxs;
- if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release))
+ /*
+ * Init percpu_ref in atomic mode so that it's faster to shutdown.
+ * See blk_register_queue() for details.
+ */
+ if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release,
+ PERCPU_REF_INIT_ATOMIC, GFP_KERNEL))
goto err_map;
setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 17f5c84ce7bf..521ae9089c50 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -551,12 +551,19 @@ int blk_register_queue(struct gendisk *disk)
return -ENXIO;
/*
- * Initialization must be complete by now. Finish the initial
- * bypass from queue allocation.
+ * SCSI probing may synchronously create and destroy a lot of
+ * request_queues for non-existent devices. Shutting down a fully
+ * functional queue takes measureable wallclock time as RCU grace
+ * periods are involved. To avoid excessive latency in these
+ * cases, a request_queue starts out in a degraded mode which is
+ * faster to shut down and is made fully functional here as
+ * request_queues for non-existent devices never get registered.
*/
if (!blk_queue_init_done(q)) {
queue_flag_set_unlocked(QUEUE_FLAG_INIT_DONE, q);
blk_queue_bypass_end(q);
+ if (q->mq_ops)
+ blk_mq_finish_init(q);
}
ret = blk_trace_init_sysfs(dev);