rcu: Provide cond_resched_rcu_qs() to force quiescent states in long loops
RCU-tasks requires the occasional voluntary context switch from CPU-bound in-kernel tasks. In some cases, this requires instrumenting cond_resched(). However, there is some reluctance to countenance unconditionally instrumenting cond_resched() (see http://lwn.net/Articles/603252/), so this commit creates a separate cond_resched_rcu_qs() that may be used in place of cond_resched() in locations prone to long-duration in-kernel looping. This commit currently instruments only RCU-tasks. Future possibilities include also instrumenting RCU, RCU-bh, and RCU-sched in order to reduce IPI usage. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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@ -367,7 +367,7 @@ static struct fdtable *close_files(struct files_struct * files)
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struct file * file = xchg(&fdt->fd[i], NULL);
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if (file) {
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filp_close(file, files);
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cond_resched();
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cond_resched_rcu_qs();
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}
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}
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i++;
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@ -330,6 +330,19 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
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#define rcu_note_voluntary_context_switch(t) do { } while (0)
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#endif /* #else #ifdef CONFIG_TASKS_RCU */
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/**
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* cond_resched_rcu_qs - Report potential quiescent states to RCU
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*
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* This macro resembles cond_resched(), except that it is defined to
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* report potential quiescent states to RCU-tasks even if the cond_resched()
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* machinery were to be shut off, as some advocate for PREEMPT kernels.
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*/
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#define cond_resched_rcu_qs() \
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do { \
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rcu_note_voluntary_context_switch(current); \
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cond_resched(); \
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} while (0)
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#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
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bool __rcu_is_watching(void);
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#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
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@ -667,7 +667,7 @@ static int rcu_torture_boost(void *arg)
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}
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call_rcu_time = jiffies;
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}
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cond_resched();
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cond_resched_rcu_qs();
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stutter_wait("rcu_torture_boost");
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if (torture_must_stop())
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goto checkwait;
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@ -1019,7 +1019,7 @@ rcu_torture_reader(void *arg)
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__this_cpu_inc(rcu_torture_batch[completed]);
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preempt_enable();
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cur_ops->readunlock(idx);
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cond_resched();
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cond_resched_rcu_qs();
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stutter_wait("rcu_torture_reader");
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} while (!torture_must_stop());
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if (irqreader && cur_ops->irq_capable) {
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@ -1647,7 +1647,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
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rnp->level, rnp->grplo,
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rnp->grphi, rnp->qsmask);
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raw_spin_unlock_irq(&rnp->lock);
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cond_resched();
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cond_resched_rcu_qs();
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}
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mutex_unlock(&rsp->onoff_mutex);
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@ -1736,7 +1736,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
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/* smp_mb() provided by prior unlock-lock pair. */
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nocb += rcu_future_gp_cleanup(rsp, rnp);
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raw_spin_unlock_irq(&rnp->lock);
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cond_resched();
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cond_resched_rcu_qs();
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}
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rnp = rcu_get_root(rsp);
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raw_spin_lock_irq(&rnp->lock);
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@ -1785,7 +1785,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
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/* Locking provides needed memory barrier. */
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if (rcu_gp_init(rsp))
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break;
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cond_resched();
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cond_resched_rcu_qs();
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flush_signals(current);
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trace_rcu_grace_period(rsp->name,
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ACCESS_ONCE(rsp->gpnum),
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@ -1828,10 +1828,10 @@ static int __noreturn rcu_gp_kthread(void *arg)
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trace_rcu_grace_period(rsp->name,
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ACCESS_ONCE(rsp->gpnum),
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TPS("fqsend"));
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cond_resched();
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cond_resched_rcu_qs();
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} else {
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/* Deal with stray signal. */
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cond_resched();
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cond_resched_rcu_qs();
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flush_signals(current);
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trace_rcu_grace_period(rsp->name,
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ACCESS_ONCE(rsp->gpnum),
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@ -2434,7 +2434,7 @@ static void force_qs_rnp(struct rcu_state *rsp,
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struct rcu_node *rnp;
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rcu_for_each_leaf_node(rsp, rnp) {
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cond_resched();
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cond_resched_rcu_qs();
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mask = 0;
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raw_spin_lock_irqsave(&rnp->lock, flags);
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smp_mb__after_unlock_lock();
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@ -1848,7 +1848,7 @@ static int rcu_oom_notify(struct notifier_block *self,
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get_online_cpus();
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for_each_online_cpu(cpu) {
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smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
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cond_resched();
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cond_resched_rcu_qs();
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}
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put_online_cpus();
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@ -789,7 +789,7 @@ static int do_mlockall(int flags)
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/* Ignore errors */
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mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
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cond_resched();
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cond_resched_rcu_qs();
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}
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out:
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return 0;
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