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Commit 19dd1591 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent adf5091e

include/linux/rcupdate.h

+2 −0
Original line number Diff line number Diff line
@@ -193,6 +193,8 @@ extern void rcu_irq_enter(void); 
extern void rcu_irq_exit(void);

extern void rcu_user_enter(void);

extern void rcu_user_exit(void);

extern void rcu_user_enter_after_irq(void);

extern void rcu_user_exit_after_irq(void);

extern void exit_rcu(void);



/**

kernel/rcutree.c

+43 −0
Original line number Diff line number Diff line
@@ -425,6 +425,27 @@ void rcu_user_enter(void) 
}





/**

 * rcu_user_enter_after_irq - inform RCU that we are going to resume userspace

 * after the current irq returns.

 *

 * This is similar to rcu_user_enter() but in the context of a non-nesting

 * irq. After this call, RCU enters into idle mode when the interrupt

 * returns.

 */

void rcu_user_enter_after_irq(void)

{

	unsigned long flags;

	struct rcu_dynticks *rdtp;



	local_irq_save(flags);

	rdtp = &__get_cpu_var(rcu_dynticks);

	/* Ensure this irq is interrupting a non-idle RCU state.  */

	WARN_ON_ONCE(!(rdtp->dynticks_nesting & DYNTICK_TASK_MASK));

	rdtp->dynticks_nesting = 1;

	local_irq_restore(flags);

}



/**

 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle

 *
@@ -549,6 +570,28 @@ void rcu_user_exit(void) 
	rcu_eqs_exit(1);

}



/**

 * rcu_user_exit_after_irq - inform RCU that we won't resume to userspace

 * idle mode after the current non-nesting irq returns.

 *

 * This is similar to rcu_user_exit() but in the context of an irq.

 * This is called when the irq has interrupted a userspace RCU idle mode

 * context. When the current non-nesting interrupt returns after this call,

 * the CPU won't restore the RCU idle mode.

 */

void rcu_user_exit_after_irq(void)

{

	unsigned long flags;

	struct rcu_dynticks *rdtp;



	local_irq_save(flags);

	rdtp = &__get_cpu_var(rcu_dynticks);

	/* Ensure we are interrupting an RCU idle mode. */

	WARN_ON_ONCE(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK);

	rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE;

	local_irq_restore(flags);

}



/**

 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle

 *