[RFC PATCH 2/7] blk-mq: add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ

[Ming Lei <ming.lei@redhat.com>]

We will stop hw queue and wait for completion of in-flight requests
when one hctx is becoming dead in the following patch. This way may
cause dead-lock for some stacking blk-mq drivers, such as dm-rq and
loop.

Add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ and mark it for dm-rq and
loop, so we needn't to wait for completion of in-flight requests of
dm-rq & loop, then the potential dead-lock can be avoided.

Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Keith Busch <keith.busch@intel.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-debugfs.c | 1 +
 drivers/block/loop.c   | 2 +-
 drivers/md/dm-rq.c     | 2 +-
 include/linux/blk-mq.h | 1 +
 4 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index af40a02c46ee..24fff8c90942 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -240,6 +240,7 @@ static const char *const hctx_flag_name[] = {
 	HCTX_FLAG_NAME(TAG_SHARED),
 	HCTX_FLAG_NAME(BLOCKING),
 	HCTX_FLAG_NAME(NO_SCHED),
+	HCTX_FLAG_NAME(NO_MANAGED_IRQ),
 };
 #undef HCTX_FLAG_NAME
 
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 44c9985f352a..199d76e8bf46 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1986,7 +1986,7 @@ static int loop_add(struct loop_device **l, int i)
 	lo->tag_set.queue_depth = 128;
 	lo->tag_set.numa_node = NUMA_NO_NODE;
 	lo->tag_set.cmd_size = sizeof(struct loop_cmd);
-	lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+	lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;
 	lo->tag_set.driver_data = lo;
 
 	err = blk_mq_alloc_tag_set(&lo->tag_set);
diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 5f7063f05ae0..f7fbef2d3cd7 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -546,7 +546,7 @@ int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)
 	md->tag_set->ops = &dm_mq_ops;
 	md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
 	md->tag_set->numa_node = md->numa_node_id;
-	md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
+	md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;
 	md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
 	md->tag_set->driver_data = md;
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3a731c3c0762..911cdc6479dc 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -219,6 +219,7 @@ struct blk_mq_ops {
 enum {
 	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,
 	BLK_MQ_F_TAG_SHARED	= 1 << 1,
+	BLK_MQ_F_NO_MANAGED_IRQ	= 1 << 2,
 	BLK_MQ_F_BLOCKING	= 1 << 5,
 	BLK_MQ_F_NO_SCHED	= 1 << 6,
 	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
-- 
2.20.1