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: a826d6dcb32d ("Btrfs: check items for correctness as we search") CC: stable@vger.kernel.org # 4.4+ Suggested-by: Qu Wenruo wqu@suse.com Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Nikolay Borisov nborisov@suse.com Signed-off-by: David Sterba dsterba@suse.com --- Hi Gregk,
Please apply this backport of upstream commit f8397d69daef06d358430d3054662fb597e37c00 to 4.9.y
fs/btrfs/disk-io.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 57d375c68e46..875715769a29 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -452,9 +452,9 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root, int mirror_num = 0; int failed_mirror = 0;
- clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags); io_tree = &BTRFS_I(root->fs_info->btree_inode)->io_tree; while (1) { + clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags); ret = read_extent_buffer_pages(io_tree, eb, WAIT_COMPLETE, btree_get_extent, mirror_num); if (!ret) { @@ -465,14 +465,6 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root, ret = -EIO; }
- /* - * This buffer's crc is fine, but its contents are corrupted, so - * there is no reason to read the other copies, they won't be - * any less wrong. - */ - if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags)) - break; - num_copies = btrfs_num_copies(root->fs_info, eb->start, eb->len); if (num_copies == 1)