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rcu: Abstract dynticks extended quiescent state enter/exit operations 

This commit is the third step towards full abstraction of all accesses
to the ->dynticks counter, implementing the previously open-coded atomic
add of 1 and entry checks in a new rcu_dynticks_eqs_enter() function, and
the same but with exit checks in a new rcu_dynticks_eqs_exit() function.
This abstraction will ease changes to the ->dynticks counter operation.

Note that this commit gets rid of the smp_mb__before_atomic() and the
smp_mb__after_atomic() calls that were previously present.  The reason
that this is OK from a memory-ordering perspective is that the atomic
operation is now atomic_add_return(), which, as a value-returning atomic,
guarantees full ordering.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Fixed RCU_TRACE() statements added by this commit. ]
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2016-11-02 14:23:30 -07:00
parent 8b2f63ab05
commit 2625d469ba
1 changed files with 62 additions and 26 deletions
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88
kernel/rcu/tree.c
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@ -281,6 +281,61 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
};
/*
* Record entry into an extended quiescent state. This is only to be
* called when not already in an extended quiescent state.
*/
static void rcu_dynticks_eqs_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int special;
/*
* CPUs seeing atomic_inc_return() must see prior RCU read-side
* critical sections, and we also must force ordering with the
* next idle sojourn.
*/
special = atomic_inc_return(&rdtp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
}
/*
* Record exit from an extended quiescent state. This is only to be
* called from an extended quiescent state.
*/
static void rcu_dynticks_eqs_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int special;
/*
* CPUs seeing atomic_inc_return() must see prior idle sojourns,
* and we also must force ordering with the next RCU read-side
* critical section.
*/
special = atomic_inc_return(&rdtp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
}
/*
* Reset the current CPU's ->dynticks counter to indicate that the
* newly onlined CPU is no longer in an extended quiescent state.
* This will either leave the counter unchanged, or increment it
* to the next non-quiescent value.
*
* The non-atomic test/increment sequence works because the upper bits
* of the ->dynticks counter are manipulated only by the corresponding CPU,
* or when the corresponding CPU is offline.
*/
static void rcu_dynticks_eqs_online(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
if (atomic_read(&rdtp->dynticks) & 0x1)
return;
atomic_add(0x1, &rdtp->dynticks);
}
/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
@ -693,7 +748,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
{
struct rcu_state *rsp;
struct rcu_data *rdp;
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)
trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
@ -712,12 +767,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
do_nocb_deferred_wakeup(rdp);
}
rcu_prepare_for_idle();
/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
smp_mb__before_atomic(); /* See above. */
atomic_inc(&rdtp->dynticks);
smp_mb__after_atomic(); /* Force ordering with next sojourn. */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
atomic_read(&rdtp->dynticks) & 0x1);
rcu_dynticks_eqs_enter();
rcu_dynticks_task_enter();
/*
@ -846,15 +896,10 @@ void rcu_irq_exit_irqson(void)
*/
static void rcu_eqs_exit_common(long long oldval, int user)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)
rcu_dynticks_task_exit();
smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */
atomic_inc(&rdtp->dynticks);
/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
smp_mb__after_atomic(); /* See above. */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
!(atomic_read(&rdtp->dynticks) & 0x1));
rcu_dynticks_eqs_exit();
rcu_cleanup_after_idle();
trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
@ -1001,11 +1046,7 @@ void rcu_nmi_enter(void)
* period (observation due to Andy Lutomirski).
*/
if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
smp_mb__before_atomic(); /* Force delay from prior write. */
atomic_inc(&rdtp->dynticks);
/* atomic_inc() before later RCU read-side crit sects */
smp_mb__after_atomic(); /* See above. */
WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
rcu_dynticks_eqs_exit();
incby = 1;
}
rdtp->dynticks_nmi_nesting += incby;
@ -1043,11 +1084,7 @@ void rcu_nmi_exit(void)
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
rdtp->dynticks_nmi_nesting = 0;
/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
smp_mb__before_atomic(); /* See above. */
atomic_inc(&rdtp->dynticks);
smp_mb__after_atomic(); /* Force delay to next write. */
WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
rcu_dynticks_eqs_enter();
}
/**
@ -3800,8 +3837,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_sysidle_init_percpu_data(rdp->dynticks);
atomic_set(&rdp->dynticks->dynticks,
(atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
rcu_dynticks_eqs_online();
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
/*