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btrfs: fix error handling when in a COW window in run_delalloc_nocow 

When run_delalloc_nocow has cow_start set to a value other than (u64)-1,
it has delayed COW writeback pending behind cur_offset.  When an error
occurs in such a window, the range going back to cow_start and not just
cur_offset needs to be unlocked, but only two error cases handle this
correctly  Move the code to handle unlock the COW range to the common
error handling label and document the logic.

To make things even more complicated, cow_file_range as called by
fallback_to_cow will unlock the range it is operating on when it fails as
well, so we need to reset cow_start right after caling fallback_to_cow
instead of only when it succeeded.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Christoph Hellwig 2023-07-24 07:22:38 -07:00 committed by David Sterba
parent 332581bde2
commit 953fa5ced5
1 changed files with 12 additions and 10 deletions
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22
fs/btrfs/inode.c
View File

@ -2029,11 +2029,8 @@ next_slot:
leaf = path->nodes[0];
if (path->slots[0] >= btrfs_header_nritems(leaf)) {
ret = btrfs_next_leaf(root, path);
if (ret < 0) {
if (cow_start != (u64)-1)
cur_offset = cow_start;
if (ret < 0)
goto error;
}
if (ret > 0)
break;
leaf = path->nodes[0];
@ -2096,13 +2093,10 @@ next_slot:
nocow_args.start = cur_offset;
ret = can_nocow_file_extent(path, &found_key, inode, &nocow_args);
if (ret < 0) {
if (cow_start != (u64)-1)
cur_offset = cow_start;
if (ret < 0)
goto error;
} else if (ret == 0) {
if (ret == 0)
goto out_check;
}
ret = 0;
bg = btrfs_inc_nocow_writers(fs_info, nocow_args.disk_bytenr);
@ -2133,9 +2127,9 @@ out_check:
if (cow_start != (u64)-1) {
ret = fallback_to_cow(inode, locked_page,
cow_start, found_key.offset - 1);
cow_start = (u64)-1;
if (ret)
goto error;
cow_start = (u64)-1;
}
nocow_end = cur_offset + nocow_args.num_bytes - 1;
@ -2214,6 +2208,7 @@ out_check:
if (cow_start != (u64)-1) {
cur_offset = end;
ret = fallback_to_cow(inode, locked_page, cow_start, end);
cow_start = (u64)-1;
if (ret)
goto error;
}
@ -2222,6 +2217,13 @@ error:
if (nocow)
btrfs_dec_nocow_writers(bg);
/*
* If an error happened while a COW region is outstanding, cur_offset
* needs to be reset to cow_start to ensure the COW region is unlocked
* as well.
*/
if (cow_start != (u64)-1)
cur_offset = cow_start;
if (ret && cur_offset < end)
extent_clear_unlock_delalloc(inode, cur_offset, end,
locked_page, EXTENT_LOCKED |