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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <netbpt5aylanmxb6pxdvvkgket7hjbtxyjyceb6h6v2yyr4tcd@rc5zbyhsms2e>
Date: Wed, 21 May 2025 16:33:35 -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 Wed, May 21, 2025 at 04:23:44PM -0700, Shakeel Butt wrote:
> 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.
> 

I think following is the simplest fix:

diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 7dd396ae3c68..aab09495192e 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -511,7 +511,10 @@ int __init ss_rstat_init(struct cgroup_subsys *ss)
 	int cpu;
 
 	if (ss) {
-		ss->rstat_ss_cpu_lock = alloc_percpu(raw_spinlock_t);
+		size_t size = sizeof(raw_spinlock_t) ?: 1;
+
+		ss->rstat_ss_cpu_lock = __alloc_percpu(size,
+						__alignof__(raw_spinlock_t));
 		if (!ss->rstat_ss_cpu_lock)
 			return -ENOMEM;
 	}