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Bhat" Subject: [PATCH v2 12/45] sched/fair: Use get/put_online_cpus_atomic() to prevent CPU offline To: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, walken@google.com, vincent.guittot@linaro.org, laijs@cn.fujitsu.com Date: Wed, 26 Jun 2013 01:57:24 +0530 Message-ID: <20130625202724.16593.64863.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> References: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13062520-2000-0000-0000-00000CA2D936 Cc: linux-arch@vger.kernel.org, nikunj@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com, linux-pm@vger.kernel.org, Peter Zijlstra , fweisbec@gmail.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, xiaoguangrong@linux.vnet.ibm.com, sbw@mit.edu, Ingo Molnar , wangyun@linux.vnet.ibm.com, "Srivatsa S. Bhat" , netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Once stop_machine() is gone from the CPU offline path, we won't be able to depend on disabling preemption to prevent CPUs from going offline from under us. Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline, while invoking from atomic context. Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Srivatsa S. Bhat --- kernel/sched/fair.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c0ac2c3..88f056e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3338,7 +3338,8 @@ done: * * Returns the target CPU number, or the same CPU if no balancing is needed. * - * preempt must be disabled. + * Must be called within get/put_online_cpus_atomic(), to prevent CPUs + * from going offline from under us. */ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) @@ -5267,6 +5268,8 @@ void idle_balance(int this_cpu, struct rq *this_rq) raw_spin_unlock(&this_rq->lock); update_blocked_averages(this_cpu); + + get_online_cpus_atomic(); rcu_read_lock(); for_each_domain(this_cpu, sd) { unsigned long interval; @@ -5290,6 +5293,7 @@ void idle_balance(int this_cpu, struct rq *this_rq) } } rcu_read_unlock(); + put_online_cpus_atomic(); raw_spin_lock(&this_rq->lock); @@ -5316,6 +5320,7 @@ static int active_load_balance_cpu_stop(void *data) struct rq *target_rq = cpu_rq(target_cpu); struct sched_domain *sd; + get_online_cpus_atomic(); raw_spin_lock_irq(&busiest_rq->lock); /* make sure the requested cpu hasn't gone down in the meantime */ @@ -5367,6 +5372,7 @@ static int active_load_balance_cpu_stop(void *data) out_unlock: busiest_rq->active_balance = 0; raw_spin_unlock_irq(&busiest_rq->lock); + put_online_cpus_atomic(); return 0; } @@ -5527,6 +5533,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle) update_blocked_averages(cpu); + get_online_cpus_atomic(); rcu_read_lock(); for_each_domain(cpu, sd) { if (!(sd->flags & SD_LOAD_BALANCE)) @@ -5575,6 +5582,7 @@ out: break; } rcu_read_unlock(); + put_online_cpus_atomic(); /* * next_balance will be updated only when there is a need. @@ -5706,6 +5714,7 @@ static void run_rebalance_domains(struct softirq_action *h) enum cpu_idle_type idle = this_rq->idle_balance ? CPU_IDLE : CPU_NOT_IDLE; + get_online_cpus_atomic(); rebalance_domains(this_cpu, idle); /* @@ -5714,6 +5723,7 @@ static void run_rebalance_domains(struct softirq_action *h) * stopped. */ nohz_idle_balance(this_cpu, idle); + put_online_cpus_atomic(); } static inline int on_null_domain(int cpu) @@ -5731,8 +5741,10 @@ void trigger_load_balance(struct rq *rq, int cpu) likely(!on_null_domain(cpu))) raise_softirq(SCHED_SOFTIRQ); #ifdef CONFIG_NO_HZ_COMMON + get_online_cpus_atomic(); if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu))) nohz_balancer_kick(cpu); + put_online_cpus_atomic(); #endif }