Re: [PATCH 14/14] block: move rq_qos_exit() into disk_release()

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On 3/4/22 08:03, Christoph Hellwig wrote:
From: Ming Lei <ming.lei@xxxxxxxxxx>

There can't be FS IO in disk_release(), so it is safe to move rq_qos_exit()
there.

The commit message only explains why it is safe to move rq_qos_exit() but not why moving that function call is useful. Please add an explanation of why moving that function call is useful and/or necessary.

diff --git a/block/genhd.c b/block/genhd.c
index 857e0a54da7dd..56f66c6fee943 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -627,7 +627,6 @@ void del_gendisk(struct gendisk *disk)
blk_mq_freeze_queue_wait(q); - rq_qos_exit(q);
  	blk_sync_queue(q);
  	blk_flush_integrity();
  	/*
@@ -1119,7 +1118,7 @@ static void disk_release_mq(struct request_queue *q)
  		elevator_exit(q);
  		mutex_unlock(&q->sysfs_lock);
  	}
-
+	rq_qos_exit(q);
  	__blk_mq_unfreeze_queue(q, true);
  }

Commit 8e141f9eb803 ("block: drain file system I/O on del_gendisk") removed the rq_qos_exit() call from blk_cleanup_queue(). This patch series does not restore the rq_qos_exit() call in blk_cleanup_queue(). I think that call should be restored since rq_qos_add() can be called before add_disk() is called. I'm referring to the following call chain:

__alloc_disk_node()
  blkcg_init_queue()
    blk_iolatency_init()
      rq_qos_add()

sd_probe() is one of the functions that can take an error path after __alloc_disk_node() has returned and before device_add_disk() is called.

Thanks,

Bart.




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