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From:   Chen Wandun <chenwandun@huawei.com>
To:     <akpm@linux-foundation.org>, <0x7f454c46@gmail.com>,
        <wangkefeng.wang@huawei.com>, <weiyongjun1@huawei.com>
CC:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Chen Wandun <chenwandun@huawei.com>
Subject: [PATCH] mm/mremap: fix memory account on do_munmap() failure
Date:   Sat, 17 Jul 2021 18:19:42 +0800
Message-ID: <20210717101942.120607-1-chenwandun@huawei.com>
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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.

Fixes: 51df7bcb6151 ("mm/mremap: account memory on do_munmap() failure")
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
---
 mm/mremap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index 5989d3990020..badfe17ade1f 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -686,7 +686,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	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;
 	}
 
-- 
2.25.1