[RFC PATCH v1 02/17] dm thin: avoid bio_set_dev under pool lock

[Yu Kuai]

From: Yu Kuai <yukuai at fygo.io>

bio_set_dev() is about to become explicitly sleepable because it can
associate the bio with a blkg for the destination queue.  pool_map()
calls bio_set_dev() while holding pool->lock with interrupts disabled,
which would be invalid once bio_set_dev() may sleep.

The lock is not needed in this map path.  The pool target is a singleton
mapping and pool_map() only reads pt->data_dev, which is a target-private
device reference acquired during construction and released during target
destruction.  It does not inspect or modify pool state protected by
pool->lock.

Remove the lock so the remap stays in the normal sleepable DM map context
while the data device pointer remains stable for the table lifetime.

Signed-off-by: Yu Kuai <yukuai at fygo.io>
---
 drivers/md/dm-thin.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 59392de7a477..358ed77ffb2b 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3438,14 +3438,11 @@ static int pool_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 static int pool_map(struct dm_target *ti, struct bio *bio)
 {
 	struct pool_c *pt = ti->private;
-	struct pool *pool = pt->pool;
 
 	/*
 	 * As this is a singleton target, ti->begin is always zero.
 	 */
-	spin_lock_irq(&pool->lock);
 	bio_set_dev(bio, pt->data_dev->bdev);
-	spin_unlock_irq(&pool->lock);
 
 	return DM_MAPIO_REMAPPED;
 }
-- 
2.51.0