If a driver sets BLK_MQ_F_BLOCKING, it is allowed to block in its
->queue_rq() handler. For that case, blk-mq ensures that we always
calls it from a safe context.

Signed-off-by: Jens Axboe <ax...@fb.com>
---
 block/blk-mq.c         | 2 +-
 include/linux/blk-mq.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c29700010b5c..eae2f12f011f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -908,7 +908,7 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool 
async)
            !blk_mq_hw_queue_mapped(hctx)))
                return;
 
-       if (!async) {
+       if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) {
                int cpu = get_cpu();
                if (cpumask_test_cpu(cpu, hctx->cpumask)) {
                        __blk_mq_run_hw_queue(hctx);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index fbcfdf323243..5daa0ef756dd 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -155,6 +155,7 @@ enum {
        BLK_MQ_F_TAG_SHARED     = 1 << 1,
        BLK_MQ_F_SG_MERGE       = 1 << 2,
        BLK_MQ_F_DEFER_ISSUE    = 1 << 4,
+       BLK_MQ_F_BLOCKING       = 1 << 5,
        BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
        BLK_MQ_F_ALLOC_POLICY_BITS = 1,
 
-- 
2.7.4

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