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blk-mq: turn WARN_ON in __blk_mq_run_hw_queue into printk

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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>
This commit is contained in:
Ming Lei 2018-01-18 00:41:52 +08:00 • committed by Jens Axboe
parent 7bed45954b
commit 7df938fbc4
1 changed files with 20 additions and 2 deletions
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22
block/blk-mq.c
View file

@ -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