ocfs2: avoid moving extents to occupied clusters

For non-auto OCFS2_IOC_MOVE_EXT operations, userspace supplies a physical
me_goal.  ocfs2_move_extent() initializes new_phys_cpos from that goal and
expects ocfs2_probe_alloc_group() to replace it with a free run in the
target block group.

The probe currently leaves *phys_cpos unchanged if the scan reaches the
end of the group without finding a free run.  An occupied goal at the last
bit can therefore survive the probe and be passed to
__ocfs2_move_extent(), which copies file data into a cluster still owned
by another inode before the bitmap is updated.

When the probe does find a free run, it also subtracts move_len from the
ending bit.  The start of an N-bit run ending at i is i - N + 1, so the
current calculation can report the bit immediately before the free run.

Clear *phys_cpos before scanning and use the correct free-run start. 
Callers already treat a zero result as -ENOSPC, so failed probes no longer
continue with an occupied caller-controlled goal.

Link: https://lore.kernel.org/20260611213510.16956-1-kylebot@openai.com
Fixes: e6b5859cccfa ("Ocfs2/move_extents: helper to probe a proper region to move in an alloc group.")
Fixes: 236b9254f8d1 ("ocfs2: fix non-auto defrag path not working issue")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions