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Btrfs: fix unfinished readahead thread for raid5/6 degraded mounting

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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@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Wang Shilong 2014-06-11 10:55:22 +08:00 committed by Chris Mason
parent cc68a8a5a4
commit 5fbc7c59fd
1 changed files with 7 additions and 2 deletions
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9
fs/btrfs/reada.c
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@ -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) {