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btrfs-progs: disk-io: Try to find a best copy when reading tree blocks 

[BUG]
If the first copy of a tree block has a bad key order, but the second
copy is completely good, then "btrfs ins dump-tree -b <bytenr>" fails to
print anything past the bad key:
  leaf 29786112 items 47 free space 983 generation 20 owner EXTENT_TREE
  leaf 29786112 flags 0x1(WRITTEN) backref revision 1
  fs uuid 3381d111-94a3-4ac7-8f39-611bbbdab7e6
  chunk uuid 9af1c3c7-2af5-488b-8553-530bd515f14c
  [snip]
  	item 9 key (20975616 METADATA_ITEM 0) itemoff 3543 itemsize 33
  		refs 1 gen 16 flags TREE_BLOCK
  		tree block skinny level 0
  		tree block backref root CHUNK_TREE
  	item 10 key (29360128 BLOCK_GROUP_ITEM 33554432) itemoff 3519 itemsize 24
  		block group used 94208 chunk_objectid 256 flags METADATA|DUP
  ERROR: leaf 29786112 slot 11 pointer invalid, offset 1245184 size 0 leaf data limit 3995
  ERROR: skip remaining slots

While kernel can locate the good copy and acts just like nothing
happened.

[CAUSE]
btrfs-progs uses read_tree_block() to try each copy. But it only uses
less strict check_tree_block(), which has less sanity check than
btrfs_check_node/leaf().

Some error like bad key order is ignored to allow btrfs check to fix it.

This leads to above problem.

[FIX]
Introduce a new member, @candidate_mirror in read_tree_block(), which
records the copy passes check_tree_block() but fails
btrfs_check_leaf/node() as last chance.

Only if no better copy found, then use @candidate_mirror.

So btrfs-progs can act just like kernel to use best copy.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=202691
Reported-by: Yoon Jungyeon <jungyeon@gatech.edu>
[Inspired by that image, not to fix any bug of that bugzilla]
Signed-off-by: Qu Wenruo <wqu@suse.com>
master
Qu Wenruo 2019-03-07 19:32:24 +08:00
parent f76136a8d0
commit 66d610010b
1 changed files with 27 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
disk-io.c
View File

@ -327,6 +327,7 @@ struct extent_buffer* read_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr,
u32 sectorsize = fs_info->sectorsize;
int mirror_num = 1;
int good_mirror = 0;
int candidate_mirror = 0;
int num_copies;
int ignore = 0;
@ -362,10 +363,30 @@ struct extent_buffer* read_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr,
&fs_info->recow_ebs);
eb->refs++;
}
btrfs_set_buffer_uptodate(eb);
return eb;
/*
* check_tree_block() is less strict to allow btrfs
* check to get raw eb with bad key order and fix it.
* But we still need to try to get a good copy if
* possible, or bad key order can go into tools like
* btrfs ins dump-tree.
*/
if (btrfs_header_level(eb))
ret = btrfs_check_node(fs_info, NULL, eb);
else
ret = btrfs_check_leaf(fs_info, NULL, eb);
if (!ret || candidate_mirror == mirror_num) {
btrfs_set_buffer_uptodate(eb);
return eb;
}
if (candidate_mirror <= 0)
candidate_mirror = mirror_num;
}
if (ignore) {
if (candidate_mirror > 0) {
mirror_num = candidate_mirror;
continue;
}
if (check_tree_block(fs_info, eb)) {
if (!fs_info->suppress_check_block_errors)
print_tree_block_error(fs_info, eb,
@ -387,7 +408,10 @@ struct extent_buffer* read_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr,
}
mirror_num++;
if (mirror_num > num_copies) {
mirror_num = good_mirror;
if (candidate_mirror > 0)
mirror_num = candidate_mirror;
else
mirror_num = good_mirror;
ignore = 1;
continue;
}