blk-mq: Always schedule hctx->next_cpu
commitc02ebfdddb
upstream. Commit0e87e58bf6
("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:0e87e58bf6
("blk-mq: improve warning for running a queue on the wrong CPU") Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -895,7 +895,7 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
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return WORK_CPU_UNBOUND;
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if (--hctx->next_cpu_batch <= 0) {
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int cpu = hctx->next_cpu, next_cpu;
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int next_cpu;
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next_cpu = cpumask_next(hctx->next_cpu, hctx->cpumask);
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if (next_cpu >= nr_cpu_ids)
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@ -903,8 +903,6 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
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hctx->next_cpu = next_cpu;
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hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
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return cpu;
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}
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return hctx->next_cpu;
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