Commit 5fbc7c59 authored Jun 11, 2014 by Wang Shilong Committed by Chris Mason Jun 13, 2014

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>

parent cc68a8a5

fs/btrfs/reada.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -428,7 +428,12 @@ static struct reada_extent reada_find_extent(struct btrfs_root root,
		continue;
		}
		if (!dev->bdev) {
		/* cannot read ahead on missing device */
		/*
		* 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 &&

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