blk-mq: rework flush sequencing logic

Witch to using a preallocated flush_rq for blk-mq similar to what's done
with the old request path.  This allows us to set up the request properly
with a tag from the actually allowed range and ->rq_disk as needed by
some drivers.  To make life easier we also switch to dynamic allocation
of ->flush_rq for the old path.

This effectively reverts most of

    "blk-mq: fix for flush deadlock"

and

    "blk-mq: Don't reserve a tag for flush request"

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 4 insertions, 12 deletions

diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 468be242db90..18ba8a627f46 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -36,15 +36,12 @@ struct blk_mq_hw_ctx {
         struct list_head        page_list;
         struct blk_mq_tags      *tags;
 
-        atomic_t                pending_flush;
-
         unsigned long           queued;
         unsigned long           run;
 #define BLK_MQ_MAX_DISPATCH_ORDER       10
         unsigned long           dispatched[BLK_MQ_MAX_DISPATCH_ORDER];
 
         unsigned int            queue_depth;
-        unsigned int            reserved_tags;
         unsigned int            numa_node;
         unsigned int            cmd_size;       /* per-request extra data */
 
@@ -129,7 +126,7 @@ void blk_mq_insert_request(struct request_queue *, struct request *,
 void blk_mq_run_queues(struct request_queue *q, bool async);
 void blk_mq_free_request(struct request *rq);
 bool blk_mq_can_queue(struct blk_mq_hw_ctx *);
-struct request *blk_mq_alloc_request(struct request_queue *q, int rw, gfp_t gfp, bool reserved);
+struct request *blk_mq_alloc_request(struct request_queue *q, int rw, gfp_t gfp);
 struct request *blk_mq_alloc_reserved_request(struct request_queue *q, int rw, gfp_t gfp);
 struct request *blk_mq_rq_from_tag(struct request_queue *q, unsigned int tag);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0375654adb28..b2d25ecbcbc1 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -101,7 +101,7 @@ struct request {
         };
         union {
                 struct call_single_data csd;
-                struct work_struct mq_flush_data;
+                struct work_struct mq_flush_work;
         };
 
         struct request_queue *q;
@@ -451,13 +451,8 @@ struct request_queue {
         unsigned long           flush_pending_since;
         struct list_head        flush_queue[2];
         struct list_head        flush_data_in_flight;
-        union {
-                struct request  flush_rq;
-                struct {
-                        spinlock_t mq_flush_lock;
-                        struct work_struct mq_flush_work;
-                };
-        };
+        struct request          *flush_rq;
+        spinlock_t              mq_flush_lock;
 
         struct mutex            sysfs_lock;