Subject: Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test'

From: Johannes Weiner <[email-masked]>
Date: Fri, 23 Jan 2015 09:18:17 -0500

Hi Guenter,

CC'ing Christoph for slub-stuff:

On Thu, Jan 22, 2015 at 09:08:02PM -0800, Guenter Roeck wrote:
> On Thu, Jan 22, 2015 at 03:05:17PM -0800, [email-masked] wrote:
> > The mm-of-the-moment snapshot 2015-01-22-15-04 has been uploaded to
> > 
> >    http://www.ozlabs.org/~akpm/mmotm/
> > 
> qemu test for ppc64 fails with
> 
> Unable to handle kernel paging request for data at address 0x0000af50
> Faulting instruction address: 0xc00000000089d5d4
> Oops: Kernel access of bad area, sig: 11 [#1]
> 
> with the following call stack:
> 
> Call Trace:
> [c00000003d32f920] [c00000000089d588] .__slab_alloc.isra.44+0x7c/0x6f4
> (unreliable)
> [c00000003d32fa90] [c00000000020cf8c] .kmem_cache_alloc_node_trace+0x12c/0x3b0
> [c00000003d32fb60] [c000000000bceeb4] .mem_cgroup_init+0x128/0x1b0
> [c00000003d32fbf0] [c00000000000a2b4] .do_one_initcall+0xd4/0x260
> [c00000003d32fce0] [c000000000ba26a8] .kernel_init_freeable+0x244/0x32c
> [c00000003d32fdb0] [c00000000000ac24] .kernel_init+0x24/0x140
> [c00000003d32fe30] [c000000000009564] .ret_from_kernel_thread+0x58/0x74
> 
> bisect log:

[...]

> # first bad commit: [a40d0d2cf21e2714e9a6c842085148c938bf36ab] mm: memcontrol: remove unnecessary soft limit tree node test

The change in question is this:

    mm: memcontrol: remove unnecessary soft limit tree node test
    
    kzalloc_node() automatically falls back to nodes with suitable memory.
    
    Signed-off-by: Johannes Weiner <[email-masked]>
    Acked-by: Michal Hocko <[email-masked]>
    Reviewed-by: Vladimir Davydov <[email-masked]>
    Signed-off-by: Andrew Morton <[email-masked]>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fb9788af4a3e..10db4a654d68 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4539,13 +4539,10 @@ static void __init mem_cgroup_soft_limit_tree_init(void)
 {
        struct mem_cgroup_tree_per_node *rtpn;
        struct mem_cgroup_tree_per_zone *rtpz;
-       int tmp, node, zone;
+       int node, zone;
 
        for_each_node(node) {
-               tmp = node;
-               if (!node_state(node, N_NORMAL_MEMORY))
-                       tmp = -1;
-               rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, tmp);
+               rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, node);
                BUG_ON(!rtpn);
 
                soft_limit_tree.rb_tree_per_node[node] = rtpn;

--

Is the assumption of this patch wrong?  Does the specified node have
to be online for the fallback to work?

Thanks