linux-kernel - [PATCH 1/1] mmap.c: find_vma: remove unnecessary if(mm) check

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Date:	Sat, 21 Apr 2012 19:12:35 +0530
From:	Rajman Mekaco <rajman.mekaco@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Rajman Mekaco <rajman.mekaco@...il.com>,
	Kautuk Consul <consul.kautuk@...il.com>
Subject: [PATCH 1/1] mmap.c: find_vma: remove unnecessary if(mm) check

The if(mm) check is not required in find_vma, as the kernel
code calls find_vma only when it is absolutely sure that the
mm_struct arg to it is non-NULL.

Removing the if(mm) check and adding the a WARN_ONCE(!mm)
for now.
This will serve the purpose of mandating that the execution
context(user-mode/kernel-mode) be known before find_vma is called.
Also fixed 2 checkpatch.pl errors in the declaration
of the rb_node and vma_tmp local variables.

I was browsing through the internet and read a discussion
at https://lkml.org/lkml/2012/3/27/342 which discusses removal
of the validation check within find_vma.
Since no-one responded, I decided to send this patch with Andrew's
suggestions.

Signed-off-by: Rajman Mekaco <rajman.mekaco@...il.com>
Cc: Kautuk Consul <consul.kautuk@...il.com>
---
 mm/mmap.c |   53 +++++++++++++++++++++++++++--------------------------
 1 files changed, 27 insertions(+), 26 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index b38b47e..1c3ef5d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1616,33 +1616,34 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 {
 	struct vm_area_struct *vma = NULL;
 
-	if (mm) {
-		/* Check the cache first. */
-		/* (Cache hit rate is typically around 35%.) */
-		vma = mm->mmap_cache;
-		if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
-			struct rb_node * rb_node;
-
-			rb_node = mm->mm_rb.rb_node;
-			vma = NULL;
-
-			while (rb_node) {
-				struct vm_area_struct * vma_tmp;
-
-				vma_tmp = rb_entry(rb_node,
-						struct vm_area_struct, vm_rb);
-
-				if (vma_tmp->vm_end > addr) {
-					vma = vma_tmp;
-					if (vma_tmp->vm_start <= addr)
-						break;
-					rb_node = rb_node->rb_left;
-				} else
-					rb_node = rb_node->rb_right;
-			}
-			if (vma)
-				mm->mmap_cache = vma;
+	if (WARN_ON_ONCE(!mm))
+		return NULL;
+
+	/* Check the cache first. */
+	/* (Cache hit rate is typically around 35%.) */
+	vma = mm->mmap_cache;
+	if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
+		struct rb_node *rb_node;
+
+		rb_node = mm->mm_rb.rb_node;
+		vma = NULL;
+
+		while (rb_node) {
+			struct vm_area_struct *vma_tmp;
+
+			vma_tmp = rb_entry(rb_node,
+					   struct vm_area_struct, vm_rb);
+
+			if (vma_tmp->vm_end > addr) {
+				vma = vma_tmp;
+				if (vma_tmp->vm_start <= addr)
+					break;
+				rb_node = rb_node->rb_left;
+			} else
+				rb_node = rb_node->rb_right;
 		}
+		if (vma)
+			mm->mmap_cache = vma;
 	}
 	return vma;
 }
-- 
1.7.5.4

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