Re: [PATCH] cgroup/kmemcheck: No need to annotate base anymore

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 2011-07-26 at 19:38 +0200, Michal Hocko wrote:
> On Tue 26-07-11 13:05:11, Steven Rostedt wrote:
> > 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.
> 
> We can still fall back to vmalloc allocation (even though it is really
> not probable that alloc_pages_exact_nid would fail that early).
> Is vmalloc a problem here? (sorry I am not familiar with kmemleak
> internals) The original code didn't distinguish kmalloc vs. vmalloc.
> 

Good question. I forgot to add the maintainer of kmemleak to the Cc
list. (fixed here).

-- Steve

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