Commit c5d900bf authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

rcu: Allow rcu_user_enter()/exit() to nest 



Allow calls to rcu_user_enter() even if we are already
in userspace (as seen by RCU) and allow calls to rcu_user_exit()
even if we are already in the kernel.

This makes the APIs more flexible to be called from architectures.
Exception entries for example won't need to know if they come from
userspace before calling rcu_user_exit().

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 2b1d5024

kernel/rcutree.c

+33 −8
Original line number Diff line number Diff line
@@ -366,11 +366,9 @@ static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval, 
 */

static void rcu_eqs_enter(bool user)

{

	unsigned long flags;

	long long oldval;

	struct rcu_dynticks *rdtp;



	local_irq_save(flags);

	rdtp = &__get_cpu_var(rcu_dynticks);

	oldval = rdtp->dynticks_nesting;

	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
@@ -379,7 +377,6 @@ static void rcu_eqs_enter(bool user) 
	else

		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;

	rcu_eqs_enter_common(rdtp, oldval, user);

	local_irq_restore(flags);

}



/**
@@ -396,7 +393,11 @@ static void rcu_eqs_enter(bool user) 
 */

void rcu_idle_enter(void)

{

	unsigned long flags;



	local_irq_save(flags);

	rcu_eqs_enter(0);

	local_irq_restore(flags);

}

EXPORT_SYMBOL_GPL(rcu_idle_enter);
@@ -411,6 +412,9 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter); 
 */

void rcu_user_enter(void)

{

	unsigned long flags;

	struct rcu_dynticks *rdtp;



	/*

	 * Some contexts may involve an exception occuring in an irq,

	 * leading to that nesting:
@@ -422,8 +426,16 @@ void rcu_user_enter(void) 
	if (in_interrupt())

		return;



	WARN_ON_ONCE(!current->mm);



	local_irq_save(flags);

	rdtp = &__get_cpu_var(rcu_dynticks);

	if (!rdtp->in_user) {

		rdtp->in_user = true;

		rcu_eqs_enter(1);

	}

	local_irq_restore(flags);

}



/**

 * rcu_user_enter_after_irq - inform RCU that we are going to resume userspace
@@ -516,11 +528,9 @@ static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval, 
 */

static void rcu_eqs_exit(bool user)

{

	unsigned long flags;

	struct rcu_dynticks *rdtp;

	long long oldval;



	local_irq_save(flags);

	rdtp = &__get_cpu_var(rcu_dynticks);

	oldval = rdtp->dynticks_nesting;

	WARN_ON_ONCE(oldval < 0);
@@ -529,7 +539,6 @@ static void rcu_eqs_exit(bool user) 
	else

		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;

	rcu_eqs_exit_common(rdtp, oldval, user);

	local_irq_restore(flags);

}



/**
@@ -545,7 +554,11 @@ static void rcu_eqs_exit(bool user) 
 */

void rcu_idle_exit(void)

{

	unsigned long flags;



	local_irq_save(flags);

	rcu_eqs_exit(0);

	local_irq_restore(flags);

}

EXPORT_SYMBOL_GPL(rcu_idle_exit);
@@ -558,6 +571,9 @@ EXPORT_SYMBOL_GPL(rcu_idle_exit); 
 */

void rcu_user_exit(void)

{

	unsigned long flags;

	struct rcu_dynticks *rdtp;



	/*

	 * Some contexts may involve an exception occuring in an irq,

	 * leading to that nesting:
@@ -569,8 +585,14 @@ void rcu_user_exit(void) 
	if (in_interrupt())

		return;



	local_irq_save(flags);

	rdtp = &__get_cpu_var(rcu_dynticks);

	if (rdtp->in_user) {

		rdtp->in_user = false;

		rcu_eqs_exit(1);

	}

	local_irq_restore(flags);

}



/**

 * rcu_user_exit_after_irq - inform RCU that we won't resume to userspace
@@ -2586,6 +2608,9 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) 
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);

	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);

	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);

#ifdef CONFIG_RCU_USER_QS

	WARN_ON_ONCE(rdp->dynticks->in_user);

#endif

	rdp->cpu = cpu;

	rdp->rsp = rsp;

	raw_spin_unlock_irqrestore(&rnp->lock, flags);

kernel/rcutree.h

+3 −0
Original line number Diff line number Diff line
@@ -102,6 +102,9 @@ struct rcu_dynticks { 
				    /* idle-period nonlazy_posted snapshot. */

	int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */

#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */

#ifdef CONFIG_RCU_USER_QS

	bool in_user;		    /* Is the CPU in userland from RCU POV? */

#endif

};



/* RCU's kthread states for tracing. */

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