[dm-devel] [PATCH 1/3] block: split having srcu from queue blocking

[Ming Lei]

Now we reuse queue flag of QUEUE_FLAG_HAS_SRCU for both having srcu and
BLK_MQ_F_BLOCKING. Actually they are two things: one is that srcu is
allocated inside queue, another is that we need to handle blocking
->queue_rq. So far this way works as expected.

dm-rq needs to set BLK_MQ_F_BLOCKING if any underlying queue is
marked as BLK_MQ_F_BLOCKING. But dm queue is allocated before tagset
is allocated, one doable way is to always allocate SRCU for dm
queue, then set BLK_MQ_F_BLOCKING for the tagset if it is required,
meantime we can mark the request queue as supporting blocking
->queue_rq.

So add one new flag of QUEUE_FLAG_BLOCKING for supporting blocking
->queue_rq only, and use one private field to describe if request
queue has allocated srcu instance.

Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 block/blk-core.c       | 2 +-
 block/blk-mq.c         | 6 +++---
 block/blk-mq.h         | 2 +-
 block/blk-sysfs.c      | 2 +-
 include/linux/blkdev.h | 5 +++--
 5 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 10619fd83c1b..7ba806a4e779 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -449,7 +449,7 @@ struct request_queue *blk_alloc_queue(int node_id, bool alloc_srcu)
 		return NULL;
 
 	if (alloc_srcu) {
-		blk_queue_flag_set(QUEUE_FLAG_HAS_SRCU, q);
+		q->has_srcu = true;
 		if (init_srcu_struct(q->srcu) != 0)
 			goto fail_q;
 	}
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0d7c9d3e0329..1408a6b8ccdc 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -259,7 +259,7 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
  */
 void blk_mq_wait_quiesce_done(struct request_queue *q)
 {
-	if (blk_queue_has_srcu(q))
+	if (blk_queue_blocking(q))
 		synchronize_srcu(q->srcu);
 	else
 		synchronize_rcu();
@@ -4024,8 +4024,8 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 		struct request_queue *q)
 {
-	WARN_ON_ONCE(blk_queue_has_srcu(q) !=
-			!!(set->flags & BLK_MQ_F_BLOCKING));
+	if (set->flags & BLK_MQ_F_BLOCKING)
+		blk_queue_flag_set(QUEUE_FLAG_BLOCKING, q);
 
 	/* mark the queue as mq asap */
 	q->mq_ops = set->ops;
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 948791ea2a3e..9601918e2034 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -377,7 +377,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 /* run the code block in @dispatch_ops with rcu/srcu read lock held */
 #define __blk_mq_run_dispatch_ops(q, check_sleep, dispatch_ops)	\
 do {								\
-	if (!blk_queue_has_srcu(q)) {				\
+	if (!blk_queue_blocking(q)) {				\
 		rcu_read_lock();				\
 		(dispatch_ops);					\
 		rcu_read_unlock();				\
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e20eadfcf5c8..af89fabb58e3 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -736,7 +736,7 @@ static void blk_free_queue_rcu(struct rcu_head *rcu_head)
 	struct request_queue *q = container_of(rcu_head, struct request_queue,
 					       rcu_head);
 
-	kmem_cache_free(blk_get_queue_kmem_cache(blk_queue_has_srcu(q)), q);
+	kmem_cache_free(blk_get_queue_kmem_cache(q->has_srcu), q);
 }
 
 /* Unconfigure the I/O scheduler and dissociate from the cgroup controller. */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c80cfaefc0a8..d84abdb294c4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -365,6 +365,7 @@ struct request_queue {
 #endif
 
 	bool			mq_sysfs_init_done;
+	bool			has_srcu;
 
 #define BLK_MAX_WRITE_HINTS	5
 	u64			write_hints[BLK_MAX_WRITE_HINTS];
@@ -385,7 +386,7 @@ struct request_queue {
 /* Keep blk_queue_flag_name[] in sync with the definitions below */
 #define QUEUE_FLAG_STOPPED	0	/* queue is stopped */
 #define QUEUE_FLAG_DYING	1	/* queue being torn down */
-#define QUEUE_FLAG_HAS_SRCU	2	/* SRCU is allocated */
+#define QUEUE_FLAG_BLOCKING	2	/* ->queue_rq may block */
 #define QUEUE_FLAG_NOMERGES     3	/* disable merge attempts */
 #define QUEUE_FLAG_SAME_COMP	4	/* complete on same CPU-group */
 #define QUEUE_FLAG_FAIL_IO	5	/* fake timeout */
@@ -423,7 +424,7 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
 
 #define blk_queue_stopped(q)	test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags)
 #define blk_queue_dying(q)	test_bit(QUEUE_FLAG_DYING, &(q)->queue_flags)
-#define blk_queue_has_srcu(q)	test_bit(QUEUE_FLAG_HAS_SRCU, &(q)->queue_flags)
+#define blk_queue_blocking(q)	test_bit(QUEUE_FLAG_BLOCKING, &(q)->queue_flags)
 #define blk_queue_dead(q)	test_bit(QUEUE_FLAG_DEAD, &(q)->queue_flags)
 #define blk_queue_init_done(q)	test_bit(QUEUE_FLAG_INIT_DONE, &(q)->queue_flags)
 #define blk_queue_nomerges(q)	test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags)
-- 
2.31.1