linux-kernel - [PATCH v2] cgroup/kmemcheck: Annotate alloc

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Date:	Tue, 26 Jul 2011 14:17:29 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Randy Dunlap <rdunlap@...otime.net>
Subject: [PATCH v2] cgroup/kmemcheck: Annotate alloc_page() for cgroup
 allocations

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() (which skips
kmemleak checks) causes a warning on boot up.

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.

If alloc_page() fails then it defaults back to vmalloc() which still
uses the kmemleak_alloc() which makes us still need the
kmemleak_not_leak() call. The solution is to call the kmemleak_alloc()
directly if the alloc_page() succeeds.

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

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 53bffc6..79c0e00 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -135,8 +135,10 @@ static void *__meminit alloc_page_cgroup(size_t size, int nid)
 	void *addr = NULL;

 	addr = alloc_pages_exact_nid(nid, size, GFP_KERNEL | __GFP_NOWARN);
-	if (addr)
+	if (addr) {
+		kmemleak_alloc(addr, size, 1, GFP_KERNEL | __GFP_NOWARN);
 		return addr;
+	}

 	if (node_state(nid, N_HIGH_MEMORY))
 		addr = vmalloc_node(size, nid);

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