Messages in this thread Patch in this message | | | From | Paolo Bonzini <> | Subject | [PATCH 2/2] blk-mq: use get_cpu/put_cpu instead of preempt_disable/preempt_enable | Date | Fri, 7 Nov 2014 23:04:00 +0100 |
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blk-mq is using preempt_disable/enable in order to ensure that the queue runners are placed on the right CPU. This does not work with the RT patches, because __blk_mq_run_hw_queue takes a non-raw spinlock with the preemption-disabled region. If there is contention on the lock, this violates the rules for preemption-disabled regions.
While this should be easily fixable within the RT patches just by doing migrate_disable/enable, we can do better and document _why_ this particular region runs with disabled preemption. After the previous patch, it is trivial to switch it to get/put_cpu; the RT patches then can change it to get_cpu_light, which lets virtio-blk run under RT kernels.
Cc: Jens Axboe <axboe@kernel.dk> Cc: Thomas Gleixner <tglx@linutronix.de> Reported-by: Clark Williams <williams@redhat.com> Tested-by: Clark Williams <williams@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- block/blk-mq.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index c6192ba78950..a958851d9dd2 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -829,14 +829,14 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) return; if (!async) { - preempt_disable(); - if (cpumask_test_cpu(smp_processor_id(), hctx->cpumask)) { + int cpu = get_cpu(); + if (cpumask_test_cpu(cpu, hctx->cpumask)) { __blk_mq_run_hw_queue(hctx); - preempt_enable(); + put_cpu(); return; } - preempt_enable(); + put_cpu(); } if (hctx->queue->nr_hw_queues == 1) -- 2.1.0
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