linux-kernel - [PATCH] cgroup/kmemcheck: No need to annotate base anymore

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Date:	Tue, 26 Jul 2011 13:05:11 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: [PATCH] cgroup/kmemcheck: No need to annotate base anymore

When the cgroup base was allocated with kmalloc, it was necessary to
annotate the variable with kmemcheck_not_leak(). But because it has
recently been changed to be allocated with alloc_page(), the annotation
is no longer needed.

I was triggering this output:

allocated 8388608 bytes of page_cgroup
please try 'cgroup_disable=memory' option if you don't want memory cgroups
kmemleak: Trying to color unknown object at 0xf5840000 as Grey
Pid: 0, comm: swapper Not tainted 3.0.0-test #12
Call Trace:
 [<c17e34e6>] ? printk+0x1d/0x1f^M
 [<c10e2941>] paint_ptr+0x4f/0x78
 [<c178ab57>] kmemleak_not_leak+0x58/0x7d
 [<c108ae9f>] ? __rcu_read_unlock+0x9/0x7d
 [<c1cdb462>] kmemleak_init+0x19d/0x1e9
 [<c1cbf771>] start_kernel+0x346/0x3ec
 [<c1cbf1b4>] ? loglevel+0x18/0x18
 [<c1cbf0aa>] i386_start_kernel+0xaa/0xb0

After a bit of debugging I tracked the object 0xf840000 (and others)
down to the cgroup code. The change from allocating base with kmalloc to
alloc_page() has the base not calling kmemleak_alloc() which adds the
pointer to the object_tree_root, but kmemleak_not_leak() adds it to the
crt_early_log[] table. On kmemleak_init(), the entry is found in the
early_log[] but not the object_tree_root, and this error message is
displayed.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 53bffc6..955a49f 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -9,7 +9,6 @@
 #include <linux/vmalloc.h>
 #include <linux/cgroup.h>
 #include <linux/swapops.h>
-#include <linux/kmemleak.h>

 static void __meminit init_page_cgroup(struct page_cgroup *pc, unsigned long id)
 {
@@ -179,13 +178,6 @@ static int __meminit init_section_page_cgroup(unsigned long pfn, int nid)
 	table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
 	base = alloc_page_cgroup(table_size, nid);

-	/*
-	 * The value stored in section->page_cgroup is (base - pfn)
-	 * and it does not point to the memory block allocated above,
-	 * causing kmemleak false positives.
-	 */
-	kmemleak_not_leak(base);
-
 	if (!base) {
 		printk(KERN_ERR "page cgroup allocation failure\n");
 		return -ENOMEM;

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