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 <wangsl.fnst@xxxxxxxxxxxxxx>
---
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
--
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