linux-kernel - [PATCH] mm: mmap: initialize align_offset explicitly for vm_unmapped

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Date:   Thu,  9 Apr 2020 18:40:35 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     willy@...radead.org, walken@...gle.com, bp@...e.de,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        jaewon31.kim@...il.com, Jaewon Kim <jaewon31.kim@...sung.com>
Subject: [PATCH] mm: mmap: initialize align_offset explicitly for
 vm_unmapped_area

On passing requirement to vm_unmapped_area, arch_get_unmapped_area and
arch_get_unmapped_area_topdown did not set align_offset. Internally on
both unmapped_area and unmapped_area_topdown, if info->align_mask is 0,
then info->align_offset was meaningless.

But commit df529cabb7a2 ("mm: mmap: add trace point of
vm_unmapped_area") always prints info->align_offset even though it is
uninitialized. Fix this uninitialized value issue by setting it to 0
explicitly.

Before
92.291104: vm_unmapped_area: addr=0x755b155000 err=0 total_vm=0x15aaf0 flags=0x1 len=0x109000 lo=0x8000 hi=0x75eed48000 mask=0x0 ofs=0x4022

After
68.584210: vm_unmapped_area: addr=0x74a4ca1000 err=0 total_vm=0x168ab1 flags=0x1 len=0x9000 lo=0x8000 hi=0x753d94b000 mask=0x0 ofs=0x0

Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
---
 mm/mmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 8d77dbbb80fe..de07bbc0e21f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2123,6 +2123,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.low_limit = mm->mmap_base;
 	info.high_limit = mmap_end;
 	info.align_mask = 0;
+	info.align_offset = 0;
 	return vm_unmapped_area(&info);
 }
 #endif
@@ -2164,6 +2165,7 @@ arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 	info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
 	info.align_mask = 0;
+	info.align_offset = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*
-- 
2.13.7