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[67.188.127.15]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-742a9829b9dsm10117474b3a.88.2025.05.21.16.47.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 May 2025 16:47:03 -0700 (PDT) Message-ID: <9151095d-98dc-4497-9a64-b2eb7f8f96ea@gmail.com> Date: Wed, 21 May 2025 16:47:01 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [OFFLIST PATCH 2/2] cgroup: use subsystem-specific rstat locks to avoid contention To: Shakeel Butt , Klara Modin Cc: Tejun Heo , Andrew Morton , Alexei Starovoitov , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Yosry Ahmed , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Vlastimil Babka , Sebastian Andrzej Siewior , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team References: <20250428174943.69803-1-inwardvessel@gmail.com> <20250428174943.69803-2-inwardvessel@gmail.com> Content-Language: en-US From: JP Kobryn In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/21/25 4:33 PM, Shakeel Butt wrote: > 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)); Thanks for narrowing this one down so fast. Would this approach be more straightforward? if (ss) { #ifdef CONFIG_SMP ss->rstat_ss_cpu_lock = alloc_percpu(raw_spinlock_t); #endif Since on non-smp the lock functions are no-ops, leaving the ss cpu lock can perhaps be left NULL. I could include a comment as well explaining why. > if (!ss->rstat_ss_cpu_lock) > return -ENOMEM; > }