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Commit 7df938fb authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

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 <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: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7bed4595

block/blk-mq.c

+20 −2
Original line number Diff line number Diff line
@@ -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.

	 */

	WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&

		cpu_online(hctx->next_cpu));

	 *

	 * 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

	 */

	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