blk-mq-sched: don't hold queue_lock when calling exit_icq

None of the other blk-mq elevator hooks are called with this lock held.
Additionally, it can lead to circular locking dependencies between
queue_lock and the private scheduler lock.

Reported-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index fe186a9eade98bf65f38070f72508619bf2d3f2b..b12f9c87b4c31cd76310dc56f8ec95c23086c7e0 100644 (file)
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -35,7 +35,10 @@ static void icq_free_icq_rcu(struct rcu_head *head)
        kmem_cache_free(icq->__rcu_icq_cache, icq);
 }
 
-/* Exit an icq. Called with both ioc and q locked. */
+/*
+ * Exit an icq. Called with both ioc and q locked for sq, only ioc locked for
+ * mq.
+ */
 static void ioc_exit_icq(struct io_cq *icq)
 {
        struct elevator_type *et = icq->q->elevator->type;
@@ -166,6 +169,7 @@ EXPORT_SYMBOL(put_io_context);
  */
 void put_io_context_active(struct io_context *ioc)
 {
+       struct elevator_type *et;
        unsigned long flags;
        struct io_cq *icq;
 
@@ -184,13 +188,19 @@ retry:
        hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
                if (icq->flags & ICQ_EXITED)
                        continue;
-               if (spin_trylock(icq->q->queue_lock)) {
+
+               et = icq->q->elevator->type;
+               if (et->uses_mq) {
                        ioc_exit_icq(icq);
-                       spin_unlock(icq->q->queue_lock);
                } else {
-                       spin_unlock_irqrestore(&ioc->lock, flags);
-                       cpu_relax();
-                       goto retry;
+                       if (spin_trylock(icq->q->queue_lock)) {
+                               ioc_exit_icq(icq);
+                               spin_unlock(icq->q->queue_lock);
+                       } else {
+                               spin_unlock_irqrestore(&ioc->lock, flags);
+                               cpu_relax();
+                               goto retry;
+                       }
                }
        }
        spin_unlock_irqrestore(&ioc->lock, flags);