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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

3 files changed, 38 insertions, 33 deletions

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 717f00854fc0..61b8d2ccc2cb 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -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);
 }
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c880f5387b1f..4c340625ffd4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -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))
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0981c0cd70fe..25e692a36280 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -158,14 +158,16 @@ 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;
-        current->rcu_read_unlock_special.b.need_qs = false;
+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;
+        }
 }
 
 /*
@@ -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;
 }