[PATCH v3 10/11] nvme/pci: don't wait for locked polling queue

There's no sense waiting for the hw queue when it currently has been
locked by another polling instance. The polling instance currently
occupying the hw queue will help reap the completion events.

It shall be safe to surrender the hw queue, as long as we could reapply
for polling later. For Synchronous polling, blk_poll() will reapply for
polling, since @spin is always True in this case. While For asynchronous
polling, i.e. io_uring itself will reapply for polling when the previous
polling returns 0.

Besides, it shall do no harm to the polling performance of mq devices.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 drivers/nvme/host/pci.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 81e6389b2042..db164fcd04e2 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c

@@ -1106,7 +1106,9 @@ static int nvme_poll(struct blk_mq_hw_ctx *hctx)
 	if (!nvme_cqe_pending(nvmeq))
 		return 0;
 
-	spin_lock(&nvmeq->cq_poll_lock);
+	if (!spin_trylock(&nvmeq->cq_poll_lock))
+		return 0;
+
 	found = nvme_process_cq(nvmeq);
 	spin_unlock(&nvmeq->cq_poll_lock);
 

-- 
2.27.0