Btrfs: fix deadlock when mounting a degraded fs

The deadlock happened when we mount degraded filesystem, the reproduced
steps are following:
 # mkfs.btrfs -f -m raid1 -d raid1 <dev0> <dev1>
 # echo 1 > /sys/block/`basename <dev0>`/device/delete
 # mount -o degraded <dev1> <mnt>

The reason was that the counter -- bi_remaining was wrong. If the missing
or unwriteable device was the last device in the mapping array, we would
not submit the original bio, so we shouldn't increase bi_remaining of it
in btrfs_end_bio(), or we would skip the final endio handle.

Fix this problem by adding a flag into btrfs bio structure. If we submit
the original bio, we will set the flag, and we increase bi_remaining counter,
or we don't.

Though there is another way to fix it -- decrease bi_remaining counter of the
original bio when we make sure the original bio is not submitted, this method
need add more check and is easy to make mistake.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 31f9036..4ca3c92 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5415,8 +5415,12 @@ static void btrfs_end_bio(struct bio *bio, int err)
                        set_bit(BIO_UPTODATE, &bio->bi_flags);
                        err = 0;
                }
+
+               if (likely(bbio->flags & BTRFS_BIO_ORIG_BIO_SUBMITTED))
+                       bio_endio_nodec(bio, err);
+               else
+                       bio_endio(bio, err);
                kfree(bbio);
-               bio_endio_nodec(bio, err);
        } else if (!is_orig_bio) {
                bio_put(bio);
        }
@@ -5671,6 +5675,7 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
                        BUG_ON(!bio); /* -ENOMEM */
                } else {
                        bio = first_bio;
+                       bbio->flags |= BTRFS_BIO_ORIG_BIO_SUBMITTED;
                }
 
                submit_stripe_bio(root, bbio, bio,

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 1a15bbe..2aaa00c 100644 (file)
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -190,11 +190,14 @@ struct btrfs_bio_stripe {
 struct btrfs_bio;
 typedef void (btrfs_bio_end_io_t) (struct btrfs_bio *bio, int err);
 
+#define BTRFS_BIO_ORIG_BIO_SUBMITTED   0x1
+
 struct btrfs_bio {
        atomic_t stripes_pending;
        struct btrfs_fs_info *fs_info;
        bio_end_io_t *end_io;
        struct bio *orig_bio;
+       unsigned long flags;
        void *private;
        atomic_t error;
        int max_errors;