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rcu: New rcu_user_enter_after_irq() and rcu_user_exit_after_irq() APIs

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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>
This commit is contained in:
Frederic Weisbecker 2012-06-04 16:42:35 -07:00
parent adf5091e6c
commit 19dd1591fc
2 changed files with 45 additions and 0 deletions
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2
include/linux/rcupdate.h
View file

@ -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);
/**

43
kernel/rcutree.c
View file

@ -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
*