Commit 0e87e58bf60e ("blk-mq: improve warning for running a queue on the
wrong CPU") attempts to avoid triggering the WARN_ON in
__blk_mq_run_hw_queue when the expected CPU is dead. Problem is, in the
last batch execution before round robin, blk_mq_hctx_next_cpu can
schedule a dead CPU and also update next_cpu to the next alive CPU in
the mask, which will trigger the WARN_ON despite the previous
workaround.
The following patch fixes this scenario by always scheduling the value
in hctx->next_cpu. This changes the moment when we round-robin the CPU
running the hctx, but it really doesn't matter, since it still executes
BLK_MQ_CPU_WORK_BATCH times in a row before switching to another CPU.
Fixes: 0e87e58bf60e ("blk-mq: improve warning for running a queue on the wrong CPU")
Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxxxxxxx>
---
block/blk-mq.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0be5577b0d56..367d21215345 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -883,7 +883,7 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
return WORK_CPU_UNBOUND;
if (--hctx->next_cpu_batch <= 0) {
- int cpu = hctx->next_cpu, next_cpu;
+ int next_cpu;
next_cpu = cpumask_next(hctx->next_cpu, hctx->cpumask);
if (next_cpu >= nr_cpu_ids)
@@ -891,8 +891,6 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
hctx->next_cpu = next_cpu;
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
-
- return cpu;
}
return hctx->next_cpu;
--
2.7.4
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