linux-kernel - Re: [OFFLIST PATCH 2/2] cgroup: use subsystem-specific rstat locks to avoid contention

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Message-ID: <a6le7a3gzao7acxzo4i2sfnoxffmz2vhd34gzlgsow4uy7lv6k@tigt33bel4fi>
Date: Wed, 21 May 2025 16:23:44 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Klara Modin <klarasmodin@...il.com>
Cc: Tejun Heo <tj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Alexei Starovoitov <ast@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	Michal Koutný <mkoutny@...e.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, JP Kobryn <inwardvessel@...il.com>, bpf@...r.kernel.org, 
	linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [OFFLIST PATCH 2/2] cgroup: use subsystem-specific rstat locks
 to avoid contention

On Thu, May 22, 2025 at 12:23:44AM +0200, Klara Modin wrote:
> Hi,
> 
> On 2025-04-28 23:15:58 -0700, Shakeel Butt wrote:
> > Please ignore this patch as it was sent by mistake.
> 
> This seems to have made it into next:
> 
> 748922dcfabd ("cgroup: use subsystem-specific rstat locks to avoid contention")
> 
> It causes a BUG and eventually a panic on my Raspberry Pi 1:
> 
> WARNING: CPU: 0 PID: 0 at mm/percpu.c:1766 pcpu_alloc_noprof (mm/percpu.c:1766 (discriminator 2)) 
> illegal size (0) or align (4) for percpu allocation

Ok this config is without CONFIG_SMP and on such configs we have:

typedef struct { } arch_spinlock_t;

So, we are doing ss->rstat_ss_cpu_lock = alloc_percpu(0).

Hmm, let me think more on how to fix this.