[PATCH 6.1 051/217] btrfs: fix wrong block_start calculation for btrfs_drop_extent_map_range()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Qu Wenruo <wqu@xxxxxxxx>

[ Upstream commit fe1c6c7acce10baf9521d6dccc17268d91ee2305 ]

[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")
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/btrfs/extent_map.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 56d7580fdc3c4..3518e638374ea 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -867,7 +867,7 @@ 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;
-- 
2.43.0







[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux