• Nikolay Borisov's avatar
    btrfs: Always try all copies when reading extent buffers · 8732a2f4
    Nikolay Borisov authored
    commit f8397d69daef06d358430d3054662fb597e37c00 upstream.
    
    When a metadata read is served the endio routine btree_readpage_end_io_hook
    is called which eventually runs the tree-checker. If tree-checker fails
    to validate the read eb then it sets EXTENT_BUFFER_CORRUPT flag. This
    leads to btree_read_extent_buffer_pages wrongly assuming that all
    available copies of this extent buffer are wrong and failing prematurely.
    Fix this modify btree_read_extent_buffer_pages to read all copies of
    the data.
    
    This failure was exhibitted in xfstests btrfs/124 which would
    spuriously fail its balance operations. The reason was that when balance
    was run following re-introduction of the missing raid1 disk
    __btrfs_map_block would map the read request to stripe 0, which
    corresponded to devid 2 (the disk which is being removed in the test):
    
        item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 3553624064) itemoff 15975 itemsize 112
    	length 1073741824 owner 2 stripe_len 65536 type DATA|RAID1
    	io_align 65536 io_width 65536 sector_size 4096
    	num_stripes 2 sub_stripes 1
    		stripe 0 devid 2 offset 2156920832
    		dev_uuid 8466c350-ed0c-4c3b-b17d-6379b445d5c8
    		stripe 1 devid 1 offset 3553624064
    		dev_uuid 1265d8db-5596-477e-af03-df08eb38d2ca
    
    This caused read requests for a checksum item that to be routed to the
    stale disk which triggered the aforementioned logic involving
    EXTENT_BUFFER_CORRUPT flag. This then triggered cascading failures of
    the balance operation.
    
    Fixes: a826d6dc ("Btrfs: check items for correctness as we search")
    CC: stable@vger.kernel.org # 4.4+
    Suggested-by: default avatarQu Wenruo <wqu@suse.com>
    Reviewed-by: default avatarQu Wenruo <wqu@suse.com>
    Signed-off-by: default avatarNikolay Borisov <nborisov@suse.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    8732a2f4
disk-io.c 121 KB