block: simplify ioc_release_fn()

Reverse double lock dancing in ioc_release_fn() can be simplified by
just using trylock on the queue_lock and back out from ioc lock on
trylock failure.  Simplify it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Tested-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 10 insertions, 36 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 811879c752e4..f53c80ecaf07 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -79,7 +79,6 @@ static void ioc_release_fn(struct work_struct *work)
 {
         struct io_context *ioc = container_of(work, struct io_context,
                                               release_work);
-        struct request_queue *last_q = NULL;
         unsigned long flags;
 
         /*
@@ -93,44 +92,19 @@ static void ioc_release_fn(struct work_struct *work)
         while (!hlist_empty(&ioc->icq_list)) {
                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
                                                 struct io_cq, ioc_node);
-                struct request_queue *this_q = icq->q;
-
-                if (this_q != last_q) {
-                        /*
-                         * Need to switch to @this_q.  Once we release
-                         * @ioc->lock, it can go away along with @cic.
-                         * Hold on to it.
-                         */
-                        __blk_get_queue(this_q);
-
-                        /*
-                         * blk_put_queue() might sleep thanks to kobject
-                         * idiocy.  Always release both locks, put and
-                         * restart.
-                         */
-                        if (last_q) {
-                                spin_unlock(last_q->queue_lock);
-                                spin_unlock_irqrestore(&ioc->lock, flags);
-                                blk_put_queue(last_q);
-                        } else {
-                                spin_unlock_irqrestore(&ioc->lock, flags);
-                        }
-
-                        last_q = this_q;
-                        spin_lock_irqsave(this_q->queue_lock, flags);
-                        spin_lock_nested(&ioc->lock, 1);
-                        continue;
+                struct request_queue *q = icq->q;
+
+                if (spin_trylock(q->queue_lock)) {
+                        ioc_exit_icq(icq);
+                        spin_unlock(q->queue_lock);
+                } else {
+                        spin_unlock_irqrestore(&ioc->lock, flags);
+                        cpu_relax();
+                        spin_lock_irqsave_nested(&ioc->lock, flags, 1);
                 }
-                ioc_exit_icq(icq);
         }
 
-        if (last_q) {
-                spin_unlock(last_q->queue_lock);
-                spin_unlock_irqrestore(&ioc->lock, flags);
-                blk_put_queue(last_q);
-        } else {
-                spin_unlock_irqrestore(&ioc->lock, flags);
-        }
+        spin_unlock_irqrestore(&ioc->lock, flags);
 
         kmem_cache_free(iocontext_cachep, ioc);
 }