blk-mq: make sure hctx->next_cpu is set correctly
When hctx->next_cpu is set from possible online CPUs, there is one
race in which hctx->next_cpu may be set as >= nr_cpu_ids, and finally
break workqueue.
The race can be triggered in the following two sitations:
1) when one CPU is becoming DEAD, blk_mq_hctx_notify_dead() is called
to dispatch requests from the DEAD cpu context, but at that
time, this DEAD CPU has been cleared from 'cpu_online_mask', so all
CPUs in hctx->cpumask may become offline, and cause hctx->next_cpu set
a bad value.
2) blk_mq_delay_run_hw_queue() is called from CPU B, and found the queue
should be run on the other CPU A, then CPU A may become offline at the
same time and all CPUs in hctx->cpumask become offline.
This patch deals with this issue by re-selecting next CPU, and making
sure it is set correctly.
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>
Reported-by: "jianchao.wang" <jianchao.w.wang@oracle.com>
Tested-by: "jianchao.wang" <jianchao.w.wang@oracle.com>
Fixes: 20e4d81393
("blk-mq: simplify queue mapping & schedule with each possisble CPU")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
parent
85cf955df8
commit
7bed45954b
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@ -1319,21 +1319,47 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
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*/
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static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
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{
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bool tried = false;
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if (hctx->queue->nr_hw_queues == 1)
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return WORK_CPU_UNBOUND;
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if (--hctx->next_cpu_batch <= 0) {
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int next_cpu;
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select_cpu:
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next_cpu = cpumask_next_and(hctx->next_cpu, hctx->cpumask,
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cpu_online_mask);
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if (next_cpu >= nr_cpu_ids)
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next_cpu = cpumask_first_and(hctx->cpumask,cpu_online_mask);
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hctx->next_cpu = next_cpu;
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/*
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* No online CPU is found, so have to make sure hctx->next_cpu
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* is set correctly for not breaking workqueue.
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*/
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if (next_cpu >= nr_cpu_ids)
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hctx->next_cpu = cpumask_first(hctx->cpumask);
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else
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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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}
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/*
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* Do unbound schedule if we can't find a online CPU for this hctx,
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* and it should only happen in the path of handling CPU DEAD.
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*/
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if (!cpu_online(hctx->next_cpu)) {
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if (!tried) {
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tried = true;
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goto select_cpu;
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}
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/*
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* Make sure to re-select CPU next time once after CPUs
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* in hctx->cpumask become online again.
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*/
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hctx->next_cpu_batch = 1;
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return WORK_CPU_UNBOUND;
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}
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return hctx->next_cpu;
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}
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