4.14-stable review patch. If anyone has any objections, please let me know.
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From: Ming Lei ming.lei@redhat.com
[ Upstream commit 7df938fbc4ee641e70e05002ac67c24b19e86e74 ]
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 borntraeger@de.ibm.com Cc: Stefan Haberland sth@linux.vnet.ibm.com Cc: Christoph Hellwig hch@lst.de Cc: Thomas Gleixner tglx@linutronix.de Cc: "jianchao.wang" jianchao.w.wang@oracle.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-mq.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)
--- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1143,9 +1143,27 @@ static void __blk_mq_run_hw_queue(struct /* * 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