btrfs: fix off-by-one in delalloc search during lseek

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: b6e83356 ("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>

fs/btrfs/extent-io-tree.c

@@ -1551,7 +1551,7 @@ u64 count_range_bits(struct extent_io_tree *tree,
 	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);

fs/btrfs/file.c

@@ -3354,7 +3354,7 @@ bool btrfs_find_delalloc_in_range(struct btrfs_inode *inode, u64 start, u64 end,
 	bool search_io_tree = true;
 	bool ret = false;
 
-	while (cur_offset < end) {
+	while (cur_offset <= end) {
 		u64 delalloc_start;
 		u64 delalloc_end;
 		bool delalloc;