linux-kernel - [PATCH 1/2 -mm] mm: brk: fix unsigned compare against 0 issue

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Date:   Fri,  5 Oct 2018 05:14:31 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     vbabka@...e.cz, kirill.shutemov@...ux.intel.com, mhocko@...nel.org,
        willy@...radead.org, ldufour@...ux.vnet.ibm.com,
        colin.king@...onical.com, akpm@...ux-foundation.org
Cc:     yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2 -mm] mm: brk: fix unsigned compare against 0 issue

Static analysis reported unsigned compare against 0 issue according to
Colin Ian King.

Defined an int temp variable to check the return value of __do_munmap().

Reported-by: Colin Ian King <colin.king@...onical.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
---
Andrew, this should be able to be folded into the original patch.

 mm/mmap.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 68dc4fb..c78f7e9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -242,17 +242,18 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long
 	 * __do_munmap() may downgrade mmap_sem to read.
 	 */
 	if (brk <= mm->brk) {
+		int ret;
 		/*
 		 * mm->brk need to be protected by write mmap_sem, update it
 		 * before downgrading mmap_sem.
 		 * When __do_munmap fail, it will be restored from origbrk.
 		 */
 		mm->brk = brk;
-		retval = __do_munmap(mm, newbrk, oldbrk-newbrk, &uf, true);
-		if (retval < 0) {
+		ret = __do_munmap(mm, newbrk, oldbrk-newbrk, &uf, true);
+		if (ret < 0) {
 			mm->brk = origbrk;
 			goto out;
-		} else if (retval == 1)
+		} else if (ret == 1)
 			downgraded = true;
 		goto success;
 	}
-- 
1.8.3.1