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




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