[PATCH v2] blk-mq: Remove 'running from the wrong CPU' warning

Daniel Wagner
2020-11-30T10:20:21Z

It's guaranteed that no request is in flight when a hctx is going
offline. This warning is only triggered when the wq's CPU is hot
plugged and the blk-mq is not synced up yet.

As this state is temporary and the request is still processed
correctly, better remove the warning as this is the fast path.

Suggested-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---

v2:
- remove the warning as suggested by Ming
v1:
- initial version
https://lore.kernel.org/linux-block/20201126095152.19151-1-dwagner@suse.de/

block/blk-mq.c | 25 -------------------------
1 file changed, 25 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 55bcee5dc032..7e6761804f86 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1495,31 +1495,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
{
int srcu_idx;

- /*
- * We should be running this queue from one of the CPUs that
- * are mapped to it.
- *
- * There are at least two related races now between setting
- * hctx->next_cpu from blk_mq_hctx_next_cpu() and running
- * __blk_mq_run_hw_queue():
- *
- * - hctx->next_cpu is found offline in blk_mq_hctx_next_cpu(),
- * but later it becomes online, then this warning is harmless
- * at all
- *
- * - hctx->next_cpu is found online in blk_mq_hctx_next_cpu(),
- * but later it becomes offline, then the warning can't be
- * triggered, and we depend on blk-mq timeout handler to
- * handle dispatched requests to this hctx
- */
- if (!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
- cpu_online(hctx->next_cpu)) {
- printk(KERN_WARNING "run queue from wrong CPU %d, hctx %s\n",
- raw_smp_processor_id(),
- cpumask_empty(hctx->cpumask) ? "inactive": "active");
- dump_stack();
- }
-
/*
* We can't run the queue inline with ints disabled. Ensure that
* we catch bad users of this early.
--
2.16.4