Normally if driver is busy to dispatch a request the logic is like below:
block layer: driver:
__blk_mq_run_hw_queue
a. blk_mq_stop_hw_queue
b. rq add to ctx->dispatch
later:
1. blk_mq_start_hw_queue
2. __blk_mq_run_hw_queue
But it's possible step 1-2 runs between a and b. And since rq isn't in
ctx->dispatch yet, step 2 will not run rq. The rq might get lost if
there are no subsequent requests kick in.
Signed-off-by: Shaohua Li <s...@fb.com>
---
block/blk-mq.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ade8a2d..e6822a2 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -772,6 +772,7 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx
*hctx)
WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));
+again:
if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
return;
@@ -853,8 +854,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx
*hctx)
*/
if (!list_empty(&rq_list)) {
spin_lock(&hctx->lock);
- list_splice(&rq_list, &hctx->dispatch);
+ list_splice_init(&rq_list, &hctx->dispatch);
spin_unlock(&hctx->lock);
+ /*
+ * the queue is expected stopped with BLK_MQ_RQ_QUEUE_BUSY, but
+ * it's possible the queue is stopped and restarted again
+ * before this. Queue restart will dispatch requests. And since
+ * requests in rq_list aren't added into hctx->dispatch yet,
+ * the requests in rq_list might get lost.
+ **/
+ goto again;
}
}
--
1.8.1
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