percpu: update free path with correct new free region

mainline inclusion
from mainline-5.2-rc1
commit 8e5a2b98
category: bugfix
bugzilla: 34611
CVE: NA

-------------------------------------------------
When updating the chunk's contig_hint on the free path of a hint that
does not touch the page boundaries, it was incorrectly using the
starting offset of the free region and the block's contig_hint. This
could lead to incorrect assumptions about fit given a size and better
alignment of the start. Fix this by using (end - start) as this is only
called when updating a hint within a block.
Signed-off-by: NDennis Zhou <dennis@kernel.org>
Reviewed-by: NPeng Fan <peng.fan@nxp.com>
(cherry picked from commit 8e5a2b98)
Signed-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/percpu.c

@@ -871,7 +871,7 @@ static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off,
 		pcpu_chunk_refresh_hint(chunk);
 	else
 		pcpu_chunk_update(chunk, pcpu_block_off_to_off(s_index, start),
-				  s_block->contig_hint);
+				  end - start);
 }
 
 /**