From e8ae577030a6c1fc8e7c8dc09920b3bd3f9d6586 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Thu, 7 Mar 2019 19:31:31 +0800 Subject: [PATCH] btrfs-progs: Use mirror_num start from 1 to avoid unnecessary retry [BUG] If the first copy of a tree block is corrupted but the other copy is good, btrfs-progs will report the error twice: checksum verify failed on 30556160 found 42A2DA71 wanted 00000000 checksum verify failed on 30556160 found 42A2DA71 wanted 00000000 While kernel only report it once, just as expected: BTRFS warning (device dm-3): dm-3 checksum verify failed on 30556160 wanted 0 found 42A2DA71 level 0 [CAUSE] We use mirror_num = 0 in read_tree_block() of btrfs-progs. At first glance it's pretty OK, but mirror num 0 in btrfs means ANY good copy. Real mirror num starts from 1. In the context of read_tree_block(), since it's read_tree_block() to do all the checks, mirror num 0 just means the first copy. So if the first copy is corrupted, btrfs-progs will try mirror num 1 next, which is just the same as mirror num 0. After reporting the same error on the same copy, btrfs-progs will finally try mirror num 2, and get the good copy. [FIX] The fix is way simpler than all the above analyse, just starts from mirror num 1. Signed-off-by: Qu Wenruo --- disk-io.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/disk-io.c b/disk-io.c index 2814b223..8b4da8f4 100644 --- a/disk-io.c +++ b/disk-io.c @@ -325,7 +325,7 @@ struct extent_buffer* read_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr, struct extent_buffer *eb; u64 best_transid = 0; u32 sectorsize = fs_info->sectorsize; - int mirror_num = 0; + int mirror_num = 1; int good_mirror = 0; int num_copies; int ignore = 0; @@ -381,7 +381,7 @@ struct extent_buffer* read_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr, ignore = 1; continue; } - if (btrfs_header_generation(eb) > best_transid && mirror_num) { + if (btrfs_header_generation(eb) > best_transid) { best_transid = btrfs_header_generation(eb); good_mirror = mirror_num; }