linux-kernel - [PATCH v2 3/3] mm/shmem: rework calculation of inflated_addr in shmem_get_unmapped

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Date:   Sun, 5 Jun 2022 11:55:57 +0800
From:   Chen Wandun <chenwandun@...wei.com>
To:     <hughd@...gle.com>, <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <willy@...radead.org>, <david@...hat.com>,
        <wangkefeng.wang@...wei.com>
Subject: [PATCH v2 3/3] mm/shmem: rework calculation of inflated_addr in shmem_get_unmapped_area

In function shmem_get_unmapped_area, inflated_offset and offset
are unsigned long, it will result in underflow when offset below
inflated_offset, a little confusing, no functional change.

Signed-off-by: Chen Wandun <chenwandun@...wei.com>
---
 mm/shmem.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 5e61692f2d8e..0b6c61a7cbb3 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2200,9 +2200,12 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 		return addr;
 
 	inflated_offset = inflated_addr & (HPAGE_PMD_SIZE-1);
-	inflated_addr += offset - inflated_offset;
-	if (inflated_offset > offset)
+	if (offset > inflated_offset)
+		inflated_addr += offset - inflated_offset;
+	else if (offset < inflated_offset) {
+		inflated_addr -= inflated_offset - offset;
 		inflated_addr += HPAGE_PMD_SIZE;
+	}
 
 	if (inflated_addr > TASK_SIZE - len)
 		return addr;
-- 
2.25.1