Btrfs: fix unfinished readahead thread for raid5/6 degraded mounting
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>
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@ -428,8 +428,13 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root,
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continue;
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}
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if (!dev->bdev) {
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/* cannot read ahead on missing device */
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continue;
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/*
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* cannot read ahead on missing device, but for RAID5/6,
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* REQ_GET_READ_MIRRORS return 1. So don't skip missing
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* device for such case.
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*/
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if (nzones > 1)
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continue;
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}
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if (dev_replace_is_ongoing &&
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dev == fs_info->dev_replace.tgtdev) {
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