From 7df938fbc4ee641e70e05002ac67c24b19e86e74 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Thu, 18 Jan 2018 00:41:52 +0800 Subject: [PATCH] blk-mq: turn WARN_ON in __blk_mq_run_hw_queue into printk We know this WARN_ON is harmless and in reality it may be trigged, so convert it to printk() and dump_stack() to avoid to confusing people. Also add comment about two releated races here. Cc: Christian Borntraeger Cc: Stefan Haberland Cc: Christoph Hellwig Cc: Thomas Gleixner Cc: "jianchao.wang" Signed-off-by: Ming Lei Signed-off-by: Jens Axboe --- block/blk-mq.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 3bd41f1066ee..ec429be05729 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1294,9 +1294,27 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) /* * 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 */ - WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) && - cpu_online(hctx->next_cpu)); + 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