btrfs: fix error handling when submitting direct I/O bio

BugLink: https://bugs.launchpad.net/bugs/1884564

[ Upstream commit 6d3113a1 ]

In btrfs_submit_direct_hook(), if a direct I/O write doesn't span a RAID
stripe or chunk, we submit orig_bio without cloning it. In this case, we
don't increment pending_bios. Then, if btrfs_submit_dio_bio() fails, we
decrement pending_bios to -1, and we never complete orig_bio. Fix it by
initializing pending_bios to 1 instead of incrementing later.

Fixing this exposes another bug: we put orig_bio prematurely and then
put it again from end_io. Fix it by not putting orig_bio.

After this change, pending_bios is really more of a reference count, but
I'll leave that cleanup separate to keep the fix small.

Fixes: e65e1535 ("btrfs: fix panic caused by direct IO")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/btrfs/inode.c

@@ -8294,7 +8294,6 @@ static int btrfs_submit_direct_hook(int rw, struct btrfs_dio_private *dip,
 	bio->bi_private = dip;
 	bio->bi_end_io = btrfs_end_dio_bio;
 	btrfs_io_bio(bio)->logical = file_offset;
-	atomic_inc(&dip->pending_bios);
 
 	while (bvec <= (orig_bio->bi_io_vec + orig_bio->bi_vcnt - 1)) {
 		if (map_length < submit_len + bvec->bv_len ||
@@ -8351,7 +8350,8 @@ static int btrfs_submit_direct_hook(int rw, struct btrfs_dio_private *dip,
 	if (!ret)
 		return 0;
 
-	bio_put(bio);
+	if (bio != orig_bio)
+		bio_put(bio);
 out_err:
 	dip->errors = 1;
 	/*
@@ -8398,7 +8398,7 @@ static void btrfs_submit_direct(int rw, struct bio *dio_bio,
 	io_bio->bi_private = dip;
 	dip->orig_bio = io_bio;
 	dip->dio_bio = dio_bio;
-	atomic_set(&dip->pending_bios, 0);
+	atomic_set(&dip->pending_bios, 1);
 	btrfs_bio = btrfs_io_bio(io_bio);
 	btrfs_bio->logical = file_offset;