diff options
author | Paolo Bonzini <pbonzini@redhat.com> | 2014-11-07 17:04:00 -0500 |
---|---|---|
committer | Jens Axboe <axboe@fb.com> | 2014-11-11 13:04:49 -0500 |
commit | 2a90d4aae5509e9cf1ba848c5d0b3458201160a0 (patch) | |
tree | f327e5db3649df99d7f957ff6932eb7e7b5fc4ed /block/blk-mq.c | |
parent | 398205b8391b208f0034a392242867b28ad8af3d (diff) |
blk-mq: use get_cpu/put_cpu instead of preempt_disable/preempt_enable
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>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq.c')
-rw-r--r-- | block/blk-mq.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index 8b309e81ed0f..06ab0683a1f1 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c | |||
@@ -802,14 +802,14 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) | |||
802 | return; | 802 | return; |
803 | 803 | ||
804 | if (!async) { | 804 | if (!async) { |
805 | preempt_disable(); | 805 | int cpu = get_cpu(); |
806 | if (cpumask_test_cpu(smp_processor_id(), hctx->cpumask)) { | 806 | if (cpumask_test_cpu(cpu, hctx->cpumask)) { |
807 | __blk_mq_run_hw_queue(hctx); | 807 | __blk_mq_run_hw_queue(hctx); |
808 | preempt_enable(); | 808 | put_cpu(); |
809 | return; | 809 | return; |
810 | } | 810 | } |
811 | 811 | ||
812 | preempt_enable(); | 812 | put_cpu(); |
813 | } | 813 | } |
814 | 814 | ||
815 | if (hctx->queue->nr_hw_queues == 1) | 815 | if (hctx->queue->nr_hw_queues == 1) |