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authorPaolo Bonzini <pbonzini@redhat.com>2014-11-08 01:04:00 +0300
committerJens Axboe <axboe@fb.com>2014-11-11 21:04:49 +0300
commit2a90d4aae5509e9cf1ba848c5d0b3458201160a0 (patch)
treef327e5db3649df99d7f957ff6932eb7e7b5fc4ed /block
parent398205b8391b208f0034a392242867b28ad8af3d (diff)
downloadlinux-2a90d4aae5509e9cf1ba848c5d0b3458201160a0.tar.xz
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')
-rw-r--r--block/blk-mq.c8
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)
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)