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rcu: New rcu_user_enter_after_irq() and rcu_user_exit_after_irq() APIs
In some cases, it is necessary to enter or exit userspace-RCU-idle mode from an interrupt handler, for example, if some other CPU sends this CPU a resched IPI. In this case, the current CPU would enter the IPI handler in userspace-RCU-idle mode, but would need to exit the IPI handler after having exited that mode. To allow this to work, this commit adds two new APIs to TREE_RCU: - rcu_user_enter_after_irq(). This must be called from an interrupt between rcu_irq_enter() and rcu_irq_exit(). After the irq calls rcu_irq_exit(), the irq handler will return into an RCU extended quiescent state. In theory, this interrupt is never a nested interrupt, but in practice it might interrupt softirq, which looks to RCU like a nested interrupt. - rcu_user_exit_after_irq(). This must be called from a non-nesting interrupt, interrupting an RCU extended quiescent state, also between rcu_irq_enter() and rcu_irq_exit(). After the irq calls rcu_irq_exit(), the irq handler will return in an RCU non-quiescent state. [ Combined with "Allow calls to rcu_exit_user_irq from nesting irqs." ] Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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@ -193,6 +193,8 @@ extern void rcu_irq_enter(void);
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extern void rcu_irq_exit(void);
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extern void rcu_user_enter(void);
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extern void rcu_user_exit(void);
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extern void rcu_user_enter_after_irq(void);
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extern void rcu_user_exit_after_irq(void);
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extern void exit_rcu(void);
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/**
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@ -425,6 +425,27 @@ void rcu_user_enter(void)
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}
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/**
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* rcu_user_enter_after_irq - inform RCU that we are going to resume userspace
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* after the current irq returns.
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*
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* This is similar to rcu_user_enter() but in the context of a non-nesting
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* irq. After this call, RCU enters into idle mode when the interrupt
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* returns.
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*/
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void rcu_user_enter_after_irq(void)
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{
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unsigned long flags;
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struct rcu_dynticks *rdtp;
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local_irq_save(flags);
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rdtp = &__get_cpu_var(rcu_dynticks);
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/* Ensure this irq is interrupting a non-idle RCU state. */
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WARN_ON_ONCE(!(rdtp->dynticks_nesting & DYNTICK_TASK_MASK));
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rdtp->dynticks_nesting = 1;
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local_irq_restore(flags);
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}
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/**
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* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
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*
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@ -549,6 +570,28 @@ void rcu_user_exit(void)
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rcu_eqs_exit(1);
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}
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/**
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* rcu_user_exit_after_irq - inform RCU that we won't resume to userspace
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* idle mode after the current non-nesting irq returns.
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*
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* This is similar to rcu_user_exit() but in the context of an irq.
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* This is called when the irq has interrupted a userspace RCU idle mode
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* context. When the current non-nesting interrupt returns after this call,
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* the CPU won't restore the RCU idle mode.
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*/
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void rcu_user_exit_after_irq(void)
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{
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unsigned long flags;
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struct rcu_dynticks *rdtp;
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local_irq_save(flags);
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rdtp = &__get_cpu_var(rcu_dynticks);
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/* Ensure we are interrupting an RCU idle mode. */
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WARN_ON_ONCE(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK);
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rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE;
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local_irq_restore(flags);
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}
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/**
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* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
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*
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