block: defer timeouts to a workqueue

Timer context is not very useful for drivers to perform any meaningful abort
action from.  So instead of calling the driver from this useless context
defer it to a workqueue as soon as possible.

Note that while a delayed_work item would seem the right thing here I didn't
dare to use it due to the magic in blk_add_timer that pokes deep into timer
internals.  But maybe this encourages Tejun to add a sensible API for that to
the workqueue API and we'll all be fine in the end :)

Contains a major update from Keith Bush:

"This patch removes synchronizing the timeout work so that the timer can
 start a freeze on its own queue. The timer enters the queue, so timer
 context can only start a freeze, but not wait for frozen."

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index 3610af561748..dd4fdfbcb3dd 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -127,13 +127,16 @@ static void blk_rq_check_expired(struct request *rq, unsigned long *next_timeout
         }
 }
 
-void blk_rq_timed_out_timer(unsigned long data)
+void blk_timeout_work(struct work_struct *work)
 {
-        struct request_queue *q = (struct request_queue *) data;
+        struct request_queue *q =
+                container_of(work, struct request_queue, timeout_work);
         unsigned long flags, next = 0;
         struct request *rq, *tmp;
         int next_set = 0;
 
+        if (blk_queue_enter(q, true))
+                return;
         spin_lock_irqsave(q->queue_lock, flags);
 
         list_for_each_entry_safe(rq, tmp, &q->timeout_list, timeout_list)
@@ -143,6 +146,7 @@ void blk_rq_timed_out_timer(unsigned long data)
                 mod_timer(&q->timeout, round_jiffies_up(next));
 
         spin_unlock_irqrestore(q->queue_lock, flags);
+        blk_queue_exit(q);
 }
 
 /**