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([2620:10d:c090:500::4:d585]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c7a8a0de11sm1099335485a.101.2025.04.16.14.43.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Apr 2025 14:43:59 -0700 (PDT) Message-ID: <88f07e01-ef0e-4e7d-933a-906c308f6ab4@gmail.com> Date: Wed, 16 Apr 2025 14:43:57 -0700 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/5] cgroup: use separate rstat trees for each subsystem To: =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: tj@kernel.org, shakeel.butt@linux.dev, yosryahmed@google.com, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@meta.com References: <20250404011050.121777-1-inwardvessel@gmail.com> <20250404011050.121777-5-inwardvessel@gmail.com> <2llytbsvkathgttzutwmrm2zwajls74p4eixxx3jyncawe5jfe@og3vps4y2tnc> Content-Language: en-US From: JP Kobryn In-Reply-To: <2llytbsvkathgttzutwmrm2zwajls74p4eixxx3jyncawe5jfe@og3vps4y2tnc> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/15/25 10:15 AM, Michal Koutný wrote: > On Thu, Apr 03, 2025 at 06:10:49PM -0700, JP Kobryn wrote: >> --- a/kernel/cgroup/cgroup.c >> +++ b/kernel/cgroup/cgroup.c > ... >> @@ -5425,6 +5417,9 @@ static void css_free_rwork_fn(struct work_struct *work) >> struct cgroup_subsys_state *parent = css->parent; >> int id = css->id; >> >> + if (ss->css_rstat_flush) >> + css_rstat_exit(css); >> + > > It should be safe to call this unguarded (see also my comment below at > css_rstat_flush()). Hmmm I checked my initial assumptions. I'm still finding that css's from any subsystem regardless of rstat usage can reach this call to exit. Without the guard there will be undefined behavior. > >> ss->css_free(css); >> cgroup_idr_remove(&ss->css_idr, id); >> cgroup_put(cgrp); >> @@ -5477,11 +5472,8 @@ static void css_release_work_fn(struct work_struct *work) >> if (ss) { >> struct cgroup *parent_cgrp; >> >> - /* css release path */ >> - if (!list_empty(&css->rstat_css_node)) { >> + if (ss->css_rstat_flush) >> css_rstat_flush(css); >> - list_del_rcu(&css->rstat_css_node); >> - } > > Ditto. Same as mentioned above, there are cases where some css's belonging to a subsystem like "cpu" (via CONFIG_CGROUP_SCHED) can reach this code. > > These conditions -- css_is_cgroup(pos) and pos->ss->css_rstat_flush > should be invariant wrt pos in the split tree, right? It's a good point. Yes, I would say so. > It's a μoptimization but may be worth checking only once before > processing the update tree? Let me do that that in the next rev.