From c02ebfdddbafa9a6a0f52fbd715e6bfa229af9d3 Mon Sep 17 00:00:00 2001 From: Gabriel Krisman Bertazi Date: Wed, 28 Sep 2016 00:24:24 -0300 Subject: [PATCH] blk-mq: Always schedule hctx->next_cpu 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 Signed-off-by: Jens Axboe --- 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 077c2416a955..6f5cb3f3dcac 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -929,7 +929,7 @@ 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) @@ -937,8 +937,6 @@ 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; -- 2.20.1