[129/212] mm/mremap: fix memory account on do_munmap() failure

Commit Message

Andrew Morton Sept. 2, 2021, 9:56 p.m. UTC

From: Chen Wandun <[e-mail]>
Subject: mm/mremap: fix memory account on do_munmap() failure

mremap will account the delta between new_len and old_len in
vma_to_resize, and then call move_vma when expanding an existing memory
mapping.  In function move_vma, there are two scenarios when calling
do_munmap:

1. move_page_tables from old_addr to new_addr success
2. move_page_tables from old_addr to new_addr fail

In first scenario, it should account old_len if do_munmap fail, because
the delta has already been accounted.

In second scenario, new_addr/new_len will assign to old_addr/old_len if
move_page_table fail, so do_munmap is try to unmap new_addr actually, if
do_munmap fail, it should account the new_len, because error code will be
return from move_vma, and delta will be unaccounted.  What'more, because
of new_len == old_len, so account old_len also is OK.

In summary, account old_len will be correct if do_munmap fail.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 51df7bcb6151 ("mm/mremap: account memory on do_munmap() failure")
Signed-off-by: Chen Wandun <[e-mail]>
Acked-by: Dmitry Safonov <[e-mail]>
Cc: Kefeng Wang <[e-mail]>
Cc: Wei Yongjun <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/mremap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

--- a/mm/mremap.c~mm-mremap-fix-memory-account-on-do_munmap-failure
+++ a/mm/mremap.c
@@ -686,7 +686,7 @@  static unsigned long move_vma(struct vm_
 	if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 		/* OOM: unable to split vma, just get accounts right */
 		if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
-			vm_acct_memory(new_len >> PAGE_SHIFT);
+			vm_acct_memory(old_len >> PAGE_SHIFT);
 		excess = 0;
 	}