linux-kernel - [PATCH] lib/scatterlist: Hook sg

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Date:	Sun, 25 Jul 2010 15:21:15 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	linux-kernel@...r.kernel.org
Cc:	Chris Wilson <chris@...is-wilson.co.uk>, Tejun Heo <tj@...nel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: [PATCH] lib/scatterlist: Hook sg_kmalloc into kmemleak

kmemleak ignores page_alloc() and so believes the final sub-page
allocation using the plain kmalloc is decoupled and lost. This leads to
lots of false-positives with code that uses scatterlists.

The options seem to be either to tell kmemleak that the kmalloc is not
leaked or to notify kmemleak of the page allocations. The danger of the
first approach is that we may hide a real leak, so choose the latter
approach (of which I am not sure of the downsides).

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Tejun Heo <tj@...nel.org>
Cc: Jens Axboe <jens.axboe@...cle.com>
Cc: Catalin Marinas <catalin.marinas@....com>
---
 lib/scatterlist.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 9afa25b..6e557b1 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -115,17 +115,20 @@ EXPORT_SYMBOL(sg_init_one);
  */
 static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
 {
-	if (nents == SG_MAX_SINGLE_ALLOC)
-		return (struct scatterlist *) __get_free_page(gfp_mask);
-	else
+	if (nents == SG_MAX_SINGLE_ALLOC) {
+		void *ptr = (void *) __get_free_page(gfp_mask);
+		kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
+		return ptr;
+	} else
 		return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
 }
 
 static void sg_kfree(struct scatterlist *sg, unsigned int nents)
 {
-	if (nents == SG_MAX_SINGLE_ALLOC)
+	if (nents == SG_MAX_SINGLE_ALLOC) {
+		kmemleak_free(sg);
 		free_page((unsigned long) sg);
-	else
+	} else
 		kfree(sg);
 }
 
-- 
1.7.1

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