Steps to reproduce: # mkfs.btrfs -f /dev/sd[b-f] -m raid5 -d raid5 # mkfs.ext4 /dev/sdc --->corrupt one of btrfs device # mount /dev/sdb /mnt -o degraded # btrfs scrub start -BRd /mnt
This is because readahead would skip missing device, this is not true for RAID5/6, because REQ_GET_READ_MIRRORS return 1 for RAID5/6 block mapping. If expected data locates in missing device, readahead thread would not call __readahead_hook() which makes event @rc->elems=0 wait forever. Fix this problem by checking return value of btrfs_map_block(),we can only skip missing device safely if there are several mirrors. Signed-off-by: Wang Shilong <[email protected]> --- fs/btrfs/reada.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c index 30947f9..09230cf 100644 --- a/fs/btrfs/reada.c +++ b/fs/btrfs/reada.c @@ -428,8 +428,13 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root, continue; } if (!dev->bdev) { - /* cannot read ahead on missing device */ - continue; + /* + * cannot read ahead on missing device, but for RAID5/6, + * REQ_GET_READ_MIRRORS return 1. So don't skip missing + * device for such case. + */ + if (nzones > 1) + continue; } if (dev_replace_is_ongoing && dev == fs_info->dev_replace.tgtdev) { -- 1.8.2.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
