[PATCH 1/4] block: more locking around delayed work

[Giuliano Procida <gprocida@google.com>]

commit 287922eb0b186e2a5bf54fdd04b734c25c90035c upstream.

The upstream commit (block: defer timeouts to a workqueue) included
various locking changes. The original commit message did not say
anything about the extra locking. Perhaps this is only needed for
workqueue callbacks and not timer callbacks. We assume it is needed
here.

This patch includes the locking changes but leaves timeouts using a
timer.

Both blk_mq_rq_timer and blk_rq_timed_out_timer will return without
without doing any work if they cannot acquire the queue (without
waiting).

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 block/blk-mq.c      | 4 ++++
 block/blk-timeout.c | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8649dbf06ce4..11a23bf73fd9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -628,6 +628,9 @@ static void blk_mq_rq_timer(unsigned long priv)
 	};
 	int i;
 
+	if (blk_queue_enter(q, GFP_NOWAIT))
+		return;
+
 	blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &data);
 
 	if (data.next_set) {
@@ -642,6 +645,7 @@ static void blk_mq_rq_timer(unsigned long priv)
 				blk_mq_tag_idle(hctx);
 		}
 	}
+	blk_queue_exit(q);
 }
 
 /*
diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index aa40aa93381b..2bc03df554a6 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -134,6 +134,8 @@ void blk_rq_timed_out_timer(unsigned long data)
 	struct request *rq, *tmp;
 	int next_set = 0;
 
+	if (blk_queue_enter(q, GFP_NOWAIT))
+		return;
 	spin_lock_irqsave(q->queue_lock, flags);
 
 	list_for_each_entry_safe(rq, tmp, &q->timeout_list, timeout_list)
@@ -143,6 +145,7 @@ 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);
 }
 
 /**
-- 
2.26.0.292.g33ef6b2f38-goog