linux-kernel - Re: [PATCH -next v2] mm/hotplug: fix a null-ptr-deref during NUMA boot

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Date:   Mon, 24 Jun 2019 16:42:20 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Qian Cai <cai@....pw>, Andrew Morton <akpm@...ux-foundation.org>,
        Barret Rhoden <brho@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ingo Molnar <mingo@...e.hu>,
        Oscar Salvador <osalvador@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next v2] mm/hotplug: fix a null-ptr-deref during NUMA boot

Hi Michal,

What about dropping the change of the online definition of your patch,
just do the following?
diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index e6dad60..9c087c3 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -749,13 +749,12 @@ static void __init init_memory_less_node(int nid)
  */
 void __init init_cpu_to_node(void)
 {
-       int cpu;
+       int cpu, node;
        u16 *cpu_to_apicid = early_per_cpu_ptr(x86_cpu_to_apicid);

        BUG_ON(cpu_to_apicid == NULL);

-       for_each_possible_cpu(cpu) {
-               int node = numa_cpu_node(cpu);
+       for_each_node_mask(node, numa_nodes_parsed) {

                if (node == NUMA_NO_NODE)
                        continue;
@@ -765,6 +764,10 @@ void __init init_cpu_to_node(void)

                numa_set_node(cpu, node);
        }
+       for_each_possible_cpu(cpu) {
+               int node = numa_cpu_node(cpu);
+               numa_set_node(cpu, node);
+       }
 }

Thanks,
  Pingfan

On Fri, Jun 21, 2019 at 9:55 PM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Fri 21-06-19 09:17:58, Qian Cai wrote:
> > Sigh...
> >
> > I don't see any benefit to keep the broken commit,
> >
> > "x86, numa: always initialize all possible nodes"
> >
> > for so long in linux-next that just prevent x86 NUMA machines with any memory-
> > less node from booting.
> >
> > Andrew, maybe it is time to drop this patch until Michal found some time to fix
> > it properly.
>
> Yes, please drop the patch for now, Andrew. I thought I could get to
> this but time is just scarce.
> --
> Michal Hocko
> SUSE Labs