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Wysocki" , kernel-team@android.com Subject: Re: [PATCH v6 08/21] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus() Message-ID: <20210521162524.22cwmrao3df7m4jb@e107158-lin.cambridge.arm.com> References: <20210518094725.7701-1-will@kernel.org> <20210518094725.7701-9-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210518094725.7701-9-will@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210521_092532_093485_19E285B7 X-CRM114-Status: GOOD ( 30.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 05/18/21 10:47, Will Deacon wrote: > Asymmetric systems may not offer the same level of userspace ISA support > across all CPUs, meaning that some applications cannot be executed by > some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do > not feature support for 32-bit applications on both clusters. > > Modify guarantee_online_cpus() to take task_cpu_possible_mask() into > account when trying to find a suitable set of online CPUs for a given > task. This will avoid passing an invalid mask to set_cpus_allowed_ptr() > during ->attach() and will subsequently allow the cpuset hierarchy to be > taken into account when forcefully overriding the affinity mask for a > task which requires migration to a compatible CPU. > > Cc: Li Zefan > Cc: Tejun Heo > Cc: Johannes Weiner > Signed-off-by: Will Deacon > --- > include/linux/cpuset.h | 2 +- > kernel/cgroup/cpuset.c | 33 +++++++++++++++++++-------------- > 2 files changed, 20 insertions(+), 15 deletions(-) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index ed6ec677dd6b..414a8e694413 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { } > static inline void cpuset_cpus_allowed(struct task_struct *p, > struct cpumask *mask) > { > - cpumask_copy(mask, cpu_possible_mask); > + cpumask_copy(mask, task_cpu_possible_mask(p)); > } > > static inline void cpuset_cpus_allowed_fallback(struct task_struct *p) > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 8c799260a4a2..b532a5333ff9 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -372,18 +372,26 @@ static inline bool is_in_v2_mode(void) > } > > /* > - * Return in pmask the portion of a cpusets's cpus_allowed that > - * are online. If none are online, walk up the cpuset hierarchy > - * until we find one that does have some online cpus. > + * Return in pmask the portion of a task's cpusets's cpus_allowed that > + * are online and are capable of running the task. If none are found, > + * walk up the cpuset hierarchy until we find one that does have some > + * appropriate cpus. > * > * One way or another, we guarantee to return some non-empty subset > * of cpu_online_mask. > * > * Call with callback_lock or cpuset_mutex held. > */ > -static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) > +static void guarantee_online_cpus(struct task_struct *tsk, > + struct cpumask *pmask) > { > - while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) { > + struct cpuset *cs = task_cs(tsk); task_cs() requires rcu_read_lock(), but I can't see how the lock is obtained from cpuset_attach() path, did I miss it? Running with lockdep should spill suspicious RCU usage warning. Maybe it makes more sense to move the rcu_read_lock() inside the function now with task_cs()? Thanks -- Qais Yousef > + const struct cpumask *possible_mask = task_cpu_possible_mask(tsk); > + > + if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask))) > + cpumask_copy(pmask, cpu_online_mask); > + > + while (!cpumask_intersects(cs->effective_cpus, pmask)) { > cs = parent_cs(cs); > if (unlikely(!cs)) { > /* > @@ -393,11 +401,10 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) > * cpuset's effective_cpus is on its way to be > * identical to cpu_online_mask. > */ > - cpumask_copy(pmask, cpu_online_mask); > return; > } > } > - cpumask_and(pmask, cs->effective_cpus, cpu_online_mask); > + cpumask_and(pmask, pmask, cs->effective_cpus); > } > > /* > @@ -2199,15 +2206,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) > > percpu_down_write(&cpuset_rwsem); > > - /* prepare for attach */ > - if (cs == &top_cpuset) > - cpumask_copy(cpus_attach, cpu_possible_mask); > - else > - guarantee_online_cpus(cs, cpus_attach); > - > guarantee_online_mems(cs, &cpuset_attach_nodemask_to); > > cgroup_taskset_for_each(task, css, tset) { > + if (cs != &top_cpuset) > + guarantee_online_cpus(task, cpus_attach); > + else > + cpumask_copy(cpus_attach, task_cpu_possible_mask(task)); > /* > * can_attach beforehand should guarantee that this doesn't > * fail. TODO: have a better way to handle failure here > @@ -3303,7 +3308,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > > spin_lock_irqsave(&callback_lock, flags); > rcu_read_lock(); > - guarantee_online_cpus(task_cs(tsk), pmask); > + guarantee_online_cpus(tsk, pmask); > rcu_read_unlock(); > spin_unlock_irqrestore(&callback_lock, flags); > } > -- > 2.31.1.751.gd2f1c929bd-goog > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel