[BUG]
During my extent_map cleanup/refactor, with extra sanity checks,
extent-map-tests::test_case_7() would not pass the checks.
The problem is, after btrfs_drop_extent_map_range(), the resulted
extent_map has a @block_start way too large.
Meanwhile my btrfs_file_extent_item based members are returning a
correct @disk_bytenr/@offset combination.
The extent map layout looks like this:
0 16K 32K 48K
| PINNED | | Regular |
The regular em at [32K, 48K) also has 32K @block_start.
Then drop range [0, 36K), which should shrink the regular one to be
[36K, 48K).
However the @block_start is incorrect, we expect 32K + 4K, but got 52K.
[CAUSE]
Inside btrfs_drop_extent_map_range() function, if we hit an extent_map
that covers the target range but is still beyond it, we need to split
that extent map into half:
|<-- drop range -->|
|<----- existing extent_map --->|
And if the extent map is not compressed, we need to forward
extent_map::block_start by the difference between the end of drop range
and the extent map start.
However in that particular case, the difference is calculated using
(start + len - em->start).
The problem is @start can be modified if the drop range covers any
pinned extent.
This leads to wrong calculation, and would be caught by my later
extent_map sanity checks, which checks the em::block_start against
btrfs_file_extent_item::disk_bytenr + btrfs_file_extent_item::offset.
This is a regression caused by commit c962098ca4af ("btrfs: fix
incorrect splitting in btrfs_drop_extent_map_range"), which removed the
@len update for pinned extents.
[FIX]
Fix it by avoiding using @start completely, and use @end - em->start
instead, which @end is exclusive bytenr number.
And update the test case to verify the @block_start to prevent such
problem from happening.
Thankfully this is not going to lead to any data corruption, as IO path
does not utilize btrfs_drop_extent_map_range() with @skip_pinned set.
So this fix is only here for the sake of consistency/correctness.
CC: stable@xxxxxxxxxxxxxxx # 6.5+
Fixes: c962098ca4af ("btrfs: fix incorrect splitting in btrfs_drop_extent_map_range")
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
Changelog:
v2:
- Remove the mention of possible corruption
Thankfully this bug does not affect IO path thus it's fine.
- Explain why c962098ca4af is the cause
---
fs/btrfs/extent_map.c | 2 +-
fs/btrfs/tests/extent-map-tests.c | 6 +++++-
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 471654cb65b0..955ce300e5a1 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -799,7 +799,7 @@ void btrfs_drop_extent_map_range(struct btrfs_inode *inode, u64 start, u64 end,
split->block_len = em->block_len;
split->orig_start = em->orig_start;
} else {
- const u64 diff = start + len - em->start;
+ const u64 diff = end - em->start;
split->block_len = split->len;
split->block_start += diff;
diff --git a/fs/btrfs/tests/extent-map-tests.c b/fs/btrfs/tests/extent-map-tests.c
index 253cce7ffecf..80e71c5cb7ab 100644
--- a/fs/btrfs/tests/extent-map-tests.c
+++ b/fs/btrfs/tests/extent-map-tests.c
@@ -818,7 +818,6 @@ static int test_case_7(struct btrfs_fs_info *fs_info)
test_err("em->len is %llu, expected 16K", em->len);
goto out;
}
-
free_extent_map(em);
read_lock(&em_tree->lock);
@@ -847,6 +846,11 @@ static int test_case_7(struct btrfs_fs_info *fs_info)
goto out;
}
+ if (em->block_start != SZ_32K + SZ_4K) {
+ test_err("em->block_start is %llu, expected 36K", em->block_start);
+ goto out;
+ }
+
free_extent_map(em);
read_lock(&em_tree->lock);
--
2.44.0
