linux-kernel - [PATCH] mm/vmalloc: a slight change of compare target in __insert_vmap

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Message-Id: <20170524100347.8131-1-richard.weiyang@gmail.com>
Date:   Wed, 24 May 2017 18:03:47 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     akpm@...ux-foundation.org, mhocko@...e.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH] mm/vmalloc: a slight change of compare target in __insert_vmap_area()

The vmap RB tree store the elements in order and no overlap between any of
them. The comparison in __insert_vmap_area() is to decide which direction
the search should follow and make sure the new vmap_area is not overlap
with any other.

Current implementation fails to do the overlap check.

When first "if" is not true, it means

    va->va_start >= tmp_va->va_end

And with the truth

    xxx->va_end > xxx->va_start

The deduction is

    va->va_end > tmp_va->va_start

which is the condition in second "if".

This patch changes a little of the comparison in __insert_vmap_area() to
make sure it forbids the overlapped vmap_area.

Signed-off-by: Wei Yang <richard.weiyang@...il.com>
---
 mm/vmalloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0b057628a7ba..8087451cb332 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -360,9 +360,9 @@ static void __insert_vmap_area(struct vmap_area *va)
 
 		parent = *p;
 		tmp_va = rb_entry(parent, struct vmap_area, rb_node);
-		if (va->va_start < tmp_va->va_end)
+		if (va->va_end <= tmp_va->va_start)
 			p = &(*p)->rb_left;
-		else if (va->va_end > tmp_va->va_start)
+		else if (va->va_start >= tmp_va->va_end)
 			p = &(*p)->rb_right;
 		else
 			BUG();
-- 
2.11.0