On 2023/12/18 23:32, Jan Kara wrote:
On Mon 18-12-23 22:18:11, Baokun Li wrote:
In ext4_move_extents(), moved_len is only updated when all moves are
successfully executed, and only discards orig_inode and donor_inode
preallocations when moved_len is not zero. When the loop fails to exit
after successfully moving some extents, moved_len is not updated and
remains at 0, so it does not discard the preallocations.
If the moved extents overlap with the preallocated extents, the
overlapped extents are freed twice in ext4_mb_release_inode_pa() and
ext4_process_freed_data() (as described in commit 94d7c16cbbbd), and
bb_free is incremented twice. Hence when trim is executed, a zero-division
bug is triggered in mb_update_avg_fragment_size() because bb_free is not
zero and bb_fragments is zero.
Therefore, update move_len after each extent move to avoid the issue.
Reported-by: Wei Chen <harperchen1110@xxxxxxxxx>
Reported-by: xingwei lee <xrivendell7@xxxxxxxxx>
Closes: https://lore.kernel.org/r/CAO4mrferzqBUnCag8R3m2zf897ts9UEuhjFQGPtODT92rYyR2Q@xxxxxxxxxxxxxx
Fixes: fcf6b1b729bc ("ext4: refactor ext4_move_extents code base")
CC: stable@xxxxxxxxxxxxxxx # 3.18
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
fs/ext4/move_extent.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 3aa57376d9c2..4b9b503c6346 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -672,7 +672,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
*/
ext4_double_up_write_data_sem(orig_inode, donor_inode);
/* Swap original branches with new branches */
- move_extent_per_page(o_filp, donor_inode,
+ *moved_len += move_extent_per_page(o_filp, donor_inode,
orig_page_index, donor_page_index,
offset_in_page, cur_len,
unwritten, &ret);
Although this is currently fine, I think ext4_move_extents() should be
careful and zero out *moved_len before it starts using it.
Totally agree, now __ext4_ioctl zeroes it out, but to avoid code logic
changes or new callers afterward, I'll zero it out before using it in
ext4_move_extents() in the next version.
@@ -682,7 +682,6 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
o_start += cur_len;
d_start += cur_len;
}
- *moved_len = o_start - orig_blk;
if (*moved_len > len)
*moved_len = len;
So I'm not sure the *moved_len > len condition can ever trigger but if it
does, we'd need to check it whenever we are returning moved_len. So either
I'd delete the condition or move it to the out label.
Honza
As the code stands now, the *moved_len > len condition never
occurs, and is supposed to be code left over from the refactoring
in [Fixes], which I'll remove in the next version.
Thank you for your review!
--
With Best Regards,
Baokun Li
.
