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[72.235.13.41]) by smtp.gmail.com with ESMTPSA id z15-20020a1709027e8f00b001c726147a45sm3126886pla.190.2023.10.18.02.35.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 02:35:27 -0700 (PDT) Sender: Tejun Heo Date: Tue, 17 Oct 2023 23:35:26 -1000 From: Tejun Heo To: Yafang Shao Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org, yosryahmed@google.com, mkoutny@suse.com, sinquersw@gmail.com, cgroups@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH bpf-next v2 1/9] cgroup: Make operations on the cgroup root_list RCU safe Message-ID: References: <20231017124546.24608-1-laoar.shao@gmail.com> <20231017124546.24608-2-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231017124546.24608-2-laoar.shao@gmail.com> X-Spam-Status: No, score=-1.5 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Tue, Oct 17, 2023 at 12:45:38PM +0000, Yafang Shao wrote: > #define for_each_root(root) \ > - list_for_each_entry((root), &cgroup_roots, root_list) > + list_for_each_entry_rcu((root), &cgroup_roots, root_list, \ > + !lockdep_is_held(&cgroup_mutex)) Shouldn't that be lockdep_is_held() without the leading negation? > @@ -1386,13 +1386,15 @@ static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset, > } > } > > - BUG_ON(!res_cgroup); > + WARN_ON_ONCE(!res_cgroup && lockdep_is_held(&cgroup_mutex)); This doesn't work. lockdep_is_held() is always true if !PROVE_LOCKING. > return res_cgroup; > } > > /* > * look up cgroup associated with current task's cgroup namespace on the > - * specified hierarchy > + * specified hierarchy. Umount synchronization is ensured via VFS layer, > + * so we don't have to hold cgroup_mutex to prevent the root from being > + * destroyed. > */ Yeah, as Michal said, let's not do it this way. Thanks. -- tejun