[PATCH V2 4/4] block: don't hold part0's refcount in IO path

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

gendisk can't be gone when there is IO activity, so not hold
part0's refcount in IO path.

Cc: Yufen Yu <yuyufen@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hou Tao <houtao1@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-core.c  | 3 ++-
 block/blk-merge.c | 3 ++-
 block/genhd.c     | 4 ++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 826a8980997d..56cc61354671 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1343,7 +1343,8 @@ void blk_account_io_done(struct request *req, u64 now)
 		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
 		part_dec_in_flight(req->q, part, rq_data_dir(req));
 
-		hd_struct_put(part);
+		if (part->partno)
+			hd_struct_put(part);
 		part_stat_unlock();
 	}
 }
diff --git a/block/blk-merge.c b/block/blk-merge.c
index a04e991b5ded..b44caa28ec04 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -672,7 +672,8 @@ static void blk_account_io_merge(struct request *req)
 
 		part_dec_in_flight(req->q, part, rq_data_dir(req));
 
-		hd_struct_put(part);
+		if (part->partno)
+			hd_struct_put(part);
 		part_stat_unlock();
 	}
 }
diff --git a/block/genhd.c b/block/genhd.c
index bf8cbb033d64..d97b95d1a2fd 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -345,7 +345,8 @@ static inline int sector_in_part(struct hd_struct *part, sector_t sector)
  *
  * CONTEXT:
  * RCU read locked.  The returned partition pointer is always valid
- * because its refcount is grabbed.
+ * because its refcount is grabbed except for part0, which lifetime
+ * is same with the disk.
  *
  * RETURNS:
  * Found partition on success, part0 is returned if no partition matches
@@ -378,7 +379,6 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
 			return part;
 		}
 	}
-	hd_struct_get(&disk->part0);
 	return &disk->part0;
 }
 
-- 
2.25.2