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-rw-r--r--block/blk-mq.c11
-rw-r--r--include/linux/percpu-refcount.h1
-rw-r--r--lib/percpu-refcount.c16
3 files changed, 27 insertions, 1 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c88e6089746d..df8e1e09dd17 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -119,7 +119,16 @@ void blk_mq_freeze_queue(struct request_queue *q)
spin_unlock_irq(q->queue_lock);
if (freeze) {
- percpu_ref_kill(&q->mq_usage_counter);
+ /*
+ * 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);
+
blk_mq_run_queues(q, false);
}
wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 3dfbf237cd8f..ef5894ca8e50 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -71,6 +71,7 @@ void percpu_ref_reinit(struct percpu_ref *ref);
void percpu_ref_exit(struct percpu_ref *ref);
void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill);
+void __percpu_ref_kill_expedited(struct percpu_ref *ref);
/**
* percpu_ref_kill - drop the initial ref
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index fe5a3342e960..a89cf09a8268 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -184,3 +184,19 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
}
EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
+
+/*
+ * XXX: Temporary kludge to work around SCSI blk-mq stall. Used only by
+ * block/blk-mq.c::blk_mq_freeze_queue(). Will be removed during v3.18
+ * devel cycle. Do not use anywhere else.
+ */
+void __percpu_ref_kill_expedited(struct percpu_ref *ref)
+{
+ WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,
+ "percpu_ref_kill() called more than once on %pf!",
+ ref->release);
+
+ ref->pcpu_count_ptr |= PCPU_REF_DEAD;
+ synchronize_sched_expedited();
+ percpu_ref_kill_rcu(&ref->rcu);
+}