The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f8397d69daef06d358430d3054662fb597e37c00 Mon Sep 17 00:00:00 2001

From: Nikolay Borisov nborisov@suse.com Date: Tue, 6 Nov 2018 16:40:20 +0200 Subject: [PATCH] btrfs: Always try all copies when reading extent buffers

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

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 3f0b6d1936e8..6d776717d8b3 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -477,9 +477,9 @@ static int btree_read_extent_buffer_pages(struct btrfs_fs_info *fs_info, int mirror_num = 0; int failed_mirror = 0;

- clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags); io_tree = &BTRFS_I(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, mirror_num); if (!ret) { @@ -493,15 +493,6 @@ static int btree_read_extent_buffer_pages(struct btrfs_fs_info *fs_info, break; }

- /* - * 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) || - ret == -EUCLEAN) - break; - num_copies = btrfs_num_copies(fs_info, eb->start, eb->len); if (num_copies == 1)