[PATCH 6.1 006/159] btrfs: fix off-by-one in delalloc search during lseek

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Filipe Manana <fdmanana@suse.com>

commit 2f2e84ca60660402bd81d0859703567c59556e6a upstream.

During lseek, when searching for delalloc in a range that represents a
hole and that range has a length of 1 byte, we end up not doing the actual
delalloc search in the inode's io tree, resulting in not correctly
reporting the offset with data or a hole. This actually only happens when
the start offset is 0 because with any other start offset we round it down
by sector size.

Reproducer:

  $ mkfs.btrfs -f /dev/sdc
  $ mount /dev/sdc /mnt/sdc

  $ xfs_io -f -c "pwrite -q 0 1" /mnt/sdc/foo

  $ xfs_io -c "seek -d 0" /mnt/sdc/foo
  Whence   Result
  DATA	   EOF

It should have reported an offset of 0 instead of EOF.

Fix this by updating btrfs_find_delalloc_in_range() and count_range_bits()
to deal with inclusive ranges properly. These functions are already
supposed to work with inclusive end offsets, they just got it wrong in a
couple places due to off-by-one mistakes.

A test case for fstests will be added later.

Reported-by: Joan Bruguera Micó <joanbrugueram@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/20221223020509.457113-1-joanbrugueram@gmail.com/
Fixes: b6e833567ea1 ("btrfs: make hole and data seeking a lot more efficient")
CC: stable@vger.kernel.org # 6.1
Tested-by: Joan Bruguera Micó <joanbrugueram@gmail.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/btrfs/extent-io-tree.c |    2 +-
 fs/btrfs/file.c           |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/fs/btrfs/extent-io-tree.c
+++ b/fs/btrfs/extent-io-tree.c
@@ -1507,7 +1507,7 @@ u64 count_range_bits(struct extent_io_tr
 	u64 last = 0;
 	int found = 0;
 
-	if (WARN_ON(search_end <= cur_start))
+	if (WARN_ON(search_end < cur_start))
 		return 0;
 
 	spin_lock(&tree->lock);
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3671,7 +3671,7 @@ bool btrfs_find_delalloc_in_range(struct
 	u64 prev_delalloc_end = 0;
 	bool ret = false;
 
-	while (cur_offset < end) {
+	while (cur_offset <= end) {
 		u64 delalloc_start;
 		u64 delalloc_end;
 		bool delalloc;