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Commit 284a8c93 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Per-CPU operation cleanups to rcu_*_qs() functions 



The rcu_bh_qs(), rcu_preempt_qs(), and rcu_sched_qs() functions use
old-style per-CPU variable access and write to ->passed_quiesce even
if it is already set.  This commit therefore updates to use the new-style
per-CPU variable access functions and avoids the spurious writes.
This commit also eliminates the "cpu" argument to these functions because
they are always invoked on the indicated CPU.

Reported-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 1d082fd0

include/linux/rcupdate.h

+2 −2
Original line number Diff line number Diff line
@@ -261,8 +261,8 @@ static inline int rcu_preempt_depth(void) 


/* Internal to kernel */

void rcu_init(void);

void rcu_sched_qs(int cpu);

void rcu_bh_qs(int cpu);

void rcu_sched_qs(void);

void rcu_bh_qs(void);

void rcu_check_callbacks(int cpu, int user);

struct notifier_block;

void rcu_idle_enter(void);

include/linux/rcutiny.h

+1 −1
Original line number Diff line number Diff line
@@ -80,7 +80,7 @@ static inline void kfree_call_rcu(struct rcu_head *head, 


static inline void rcu_note_context_switch(int cpu)

{

	rcu_sched_qs(cpu);

	rcu_sched_qs();

}



/*

kernel/rcu/tiny.c

+5 −5
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ static void rcu_idle_enter_common(long long newval) 
			  current->pid, current->comm,

			  idle->pid, idle->comm); /* must be idle task! */

	}

	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */

	rcu_sched_qs(); /* implies rcu_bh_inc() */

	barrier();

	rcu_dynticks_nesting = newval;

}
@@ -217,7 +217,7 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 
 * are at it, given that any rcu quiescent state is also an rcu_bh

 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.

 */

void rcu_sched_qs(int cpu)

void rcu_sched_qs(void)

{

	unsigned long flags;
@@ -231,7 +231,7 @@ void rcu_sched_qs(int cpu) 
/*

 * Record an rcu_bh quiescent state.

 */

void rcu_bh_qs(int cpu)

void rcu_bh_qs(void)

{

	unsigned long flags;
@@ -251,9 +251,9 @@ void rcu_check_callbacks(int cpu, int user) 
{

	RCU_TRACE(check_cpu_stalls());

	if (user || rcu_is_cpu_rrupt_from_idle())

		rcu_sched_qs(cpu);

		rcu_sched_qs();

	else if (!in_softirq())

		rcu_bh_qs(cpu);

		rcu_bh_qs();

	if (user)

		rcu_note_voluntary_context_switch(current);

}

kernel/rcu/tree.c

+18 −16
Original line number Diff line number Diff line
@@ -188,22 +188,24 @@ static int rcu_gp_in_progress(struct rcu_state *rsp) 
 * one since the start of the grace period, this just sets a flag.

 * The caller must have disabled preemption.

 */

void rcu_sched_qs(int cpu)

void rcu_sched_qs(void)

{

	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);



	if (rdp->passed_quiesce == 0)

		trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));

	rdp->passed_quiesce = 1;

	if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {

		trace_rcu_grace_period(TPS("rcu_sched"),

				       __this_cpu_read(rcu_sched_data.gpnum),

				       TPS("cpuqs"));

		__this_cpu_write(rcu_sched_data.passed_quiesce, 1);

	}

}



void rcu_bh_qs(int cpu)

void rcu_bh_qs(void)

{

	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);



	if (rdp->passed_quiesce == 0)

		trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));

	rdp->passed_quiesce = 1;

	if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {

		trace_rcu_grace_period(TPS("rcu_bh"),

				       __this_cpu_read(rcu_bh_data.gpnum),

				       TPS("cpuqs"));

		__this_cpu_write(rcu_bh_data.passed_quiesce, 1);

	}

}



static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
@@ -278,7 +280,7 @@ static void rcu_momentary_dyntick_idle(void) 
void rcu_note_context_switch(int cpu)

{

	trace_rcu_utilization(TPS("Start context switch"));

	rcu_sched_qs(cpu);

	rcu_sched_qs();

	rcu_preempt_note_context_switch(cpu);

	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))

		rcu_momentary_dyntick_idle();
@@ -2395,8 +2397,8 @@ void rcu_check_callbacks(int cpu, int user) 
		 * at least not while the corresponding CPU is online.

		 */



		rcu_sched_qs(cpu);

		rcu_bh_qs(cpu);

		rcu_sched_qs();

		rcu_bh_qs();



	} else if (!in_softirq()) {
@@ -2407,7 +2409,7 @@ void rcu_check_callbacks(int cpu, int user) 
		 * critical section, so note it.

		 */



		rcu_bh_qs(cpu);

		rcu_bh_qs();

	}

	rcu_preempt_check_callbacks(cpu);

	if (rcu_pending(cpu))

kernel/rcu/tree_plugin.h

+15 −12
Original line number Diff line number Diff line
@@ -158,15 +158,17 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed); 
 * As with the other rcu_*_qs() functions, callers to this function

 * must disable preemption.

 */

static void rcu_preempt_qs(int cpu)

{

	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);



	if (rdp->passed_quiesce == 0)

		trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));

	rdp->passed_quiesce = 1;

static void rcu_preempt_qs(void)

{

	if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {

		trace_rcu_grace_period(TPS("rcu_preempt"),

				       __this_cpu_read(rcu_preempt_data.gpnum),

				       TPS("cpuqs"));

		__this_cpu_write(rcu_preempt_data.passed_quiesce, 1);

		barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */

		current->rcu_read_unlock_special.b.need_qs = false;

	}

}



/*

 * We have entered the scheduler, and the current task might soon be
@@ -256,7 +258,7 @@ static void rcu_preempt_note_context_switch(int cpu) 
	 * grace period, then the fact that the task has been enqueued

	 * means that we continue to block the current grace period.

	 */

	rcu_preempt_qs(cpu);

	rcu_preempt_qs();

}



/*
@@ -352,7 +354,7 @@ void rcu_read_unlock_special(struct task_struct *t) 
	 */

	special = t->rcu_read_unlock_special;

	if (special.b.need_qs) {

		rcu_preempt_qs(smp_processor_id());

		rcu_preempt_qs();

		if (!t->rcu_read_unlock_special.s) {

			local_irq_restore(flags);

			return;
@@ -651,11 +653,12 @@ static void rcu_preempt_check_callbacks(int cpu) 
	struct task_struct *t = current;



	if (t->rcu_read_lock_nesting == 0) {

		rcu_preempt_qs(cpu);

		rcu_preempt_qs();

		return;

	}

	if (t->rcu_read_lock_nesting > 0 &&

	    per_cpu(rcu_preempt_data, cpu).qs_pending)

	    per_cpu(rcu_preempt_data, cpu).qs_pending &&

	    !per_cpu(rcu_preempt_data, cpu).passed_quiesce)

		t->rcu_read_unlock_special.b.need_qs = true;

}