linux-kernel - Re: [PATCH 0/2] mm/page_alloc: Remote per-cpu lists drain support

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Message-ID: <b5363ced8e17d07d41554da8fde06c410e6688e0.camel@redhat.com>
Date:   Wed, 09 Feb 2022 10:45:00 +0100
From:   Nicolas Saenz Julienne <nsaenzju@...hat.com>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        frederic@...nel.org, tglx@...utronix.de, mtosatti@...hat.com,
        mgorman@...e.de, linux-rt-users@...r.kernel.org, vbabka@...e.cz,
        cl@...ux.com, paulmck@...nel.org, willy@...radead.org
Subject: Re: [PATCH 0/2] mm/page_alloc: Remote per-cpu lists drain support

Hi Xiongfeng, thanks for taking the time to look at this.

On Wed, 2022-02-09 at 16:55 +0800, Xiongfeng Wang wrote:
> Hi Nicolas，
> 
> When I applied the patchset on the following commit and tested on QEMU, I came
> accross the following CallTrace.
>   commit dd81e1c7d5fb126e5fbc5c9e334d7b3ec29a16a0
> 
> I wrote a userspace application to consume the memory. When the memory is used
> out, the OOM killer is triggered and the following Calltrace is printed. I am
> not sure if it is related to this patchset. But when I reverted this patchset,
> the 'NULL pointer' Calltrace didn't show.

It's a silly mistake on my part, while cleaning up the code I messed up one of
the 'struct per_cpu_pages' accessors. This should fix it:

------------------------->8-------------------------
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0caa7155ca34..e65b991c3dc8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3279,7 +3279,7 @@ static void __drain_all_pages(struct zone *zone, bool force_all_cpus)
                                has_pcps = true;
                } else {
                        for_each_populated_zone(z) {
-                               pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
+                               pcp = per_cpu_ptr(z->per_cpu_pageset, cpu);
                                lp = rcu_dereference_protected(pcp->lp,
                                                mutex_is_locked(&pcpu_drain_mutex));
                                if (lp->count) {
------------------------->8-------------------------

Thanks!

-- 
Nicolás Sáenz