Re: [PATCH v3] cgroup/kmemcheck: Annotate alloc_page() for cgroup allocations

[Johannes Weiner <hannes@cmpxchg.org>]

On Tue, Jul 26, 2011 at 03:19:16PM -0400, 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() (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.
> 
> Reviewed-by: Michal Hocko <mhocko@suse.cz>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>