[PATCH] btrfs: Check for missing device before bio submission in btrfs_map_bio

[Nikolay Borisov <nborisov@suse.com>]

Before btrfs_map_bio submits all stripe bio it does a number of checks
to ensure the device for every stripe is present. However, it doesn't
do a DEV_STATE_MISSING check, instead this is relegated to the lower
level btrfs_schedule_bio (in the async submission case, sync submission
doesn't check DEV_STATE_MISSING at all). Additionally
btrfs_schedule_bios does the duplicate device->bdev check which has
already been performed in btrfs_map_bio.

This patch moves the DEV_STATE_MISSING check in btrfs_map_bio and
removes the duplicate device->bdev check. Doing so ensures that no bio
cloning/submission happens for both async/sync requests in the face of
missing device. This makes the async io submission path slightly shorter
in terms of instruction count. No functional changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/volumes.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 44c5e8ccb644..3312cad65209 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6106,12 +6106,6 @@ static noinline void btrfs_schedule_bio(struct btrfs_device *device,
 	int should_queue = 1;
 	struct btrfs_pending_bios *pending_bios;
 
-	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state) ||
-	    !device->bdev) {
-		bio_io_error(bio);
-		return;
-	}
-
 	/* don't bother with additional async steps for reads, right now */
 	if (bio_op(bio) == REQ_OP_READ) {
 		btrfsic_submit_bio(bio);
@@ -6240,7 +6234,8 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 
 	for (dev_nr = 0; dev_nr < total_devs; dev_nr++) {
 		dev = bbio->stripes[dev_nr].dev;
-		if (!dev || !dev->bdev ||
+		if (!dev || !dev->bdev || test_bit(BTRFS_DEV_STATE_MISSING,
+						   &dev->dev_state) ||
 		    (bio_op(first_bio) == REQ_OP_WRITE &&
 		    !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state))) {
 			bbio_error(bbio, first_bio, logical);
-- 
2.17.1