rcu: Deconfuse dynticks entry-exit tracing

The trace_rcu_dyntick() trace event did not print both the old and
the new value of the nesting level, and furthermore printed only
the low-order 32 bits of it.  This could result in some confusion
when interpreting trace-event dumps, so this commit prints both
the old and the new value, prints the full 64 bits, and also selects
the process-entry/exit increment to print nicely in hexadecimal.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

3 files changed, 44 insertions, 26 deletions

diff --git a/kernel/rcu.h b/kernel/rcu.h
index f600868d550d..aa88baab5f78 100644
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -30,6 +30,13 @@
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
 
 /*
+ * Process-level increment to ->dynticks_nesting field.  This allows for
+ * architectures that use half-interrupts and half-exceptions from
+ * process context.
+ */
+#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1)
+
+/*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
  * by call_rcu() and rcu callback execution, and are therefore not part of the
  * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index b4e0b4981768..9b9bdf666fb5 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -53,20 +53,21 @@ static void __call_rcu(struct rcu_head *head,
 
 #include "rcutiny_plugin.h"
 
-static long long rcu_dynticks_nesting = LLONG_MAX / 2;
+static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
 
 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
-static void rcu_idle_enter_common(void)
+static void rcu_idle_enter_common(long long oldval)
 {
         if (rcu_dynticks_nesting) {
-                RCU_TRACE(trace_rcu_dyntick("--=", rcu_dynticks_nesting));
+                RCU_TRACE(trace_rcu_dyntick("--=",
+                                            oldval, rcu_dynticks_nesting));
                 return;
         }
-        RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting));
+        RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
         if (!idle_cpu(smp_processor_id())) {
                 WARN_ON_ONCE(1);        /* must be idle task! */
                 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
-                                            rcu_dynticks_nesting));
+                                            oldval, rcu_dynticks_nesting));
                 ftrace_dump(DUMP_ALL);
         }
         rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
@@ -79,10 +80,12 @@ static void rcu_idle_enter_common(void)
 void rcu_idle_enter(void)
 {
         unsigned long flags;
+        long long oldval;
 
         local_irq_save(flags);
+        oldval = rcu_dynticks_nesting;
         rcu_dynticks_nesting = 0;
-        rcu_idle_enter_common();
+        rcu_idle_enter_common(oldval);
         local_irq_restore(flags);
 }
 
@@ -92,11 +95,13 @@ void rcu_idle_enter(void)
 void rcu_irq_exit(void)
 {
         unsigned long flags;
+        long long oldval;
 
         local_irq_save(flags);
+        oldval = rcu_dynticks_nesting;
         rcu_dynticks_nesting--;
         WARN_ON_ONCE(rcu_dynticks_nesting < 0);
-        rcu_idle_enter_common();
+        rcu_idle_enter_common(oldval);
         local_irq_restore(flags);
 }
 
@@ -104,14 +109,15 @@ void rcu_irq_exit(void)
 static void rcu_idle_exit_common(long long oldval)
 {
         if (oldval) {
-                RCU_TRACE(trace_rcu_dyntick("++=", rcu_dynticks_nesting));
+                RCU_TRACE(trace_rcu_dyntick("++=",
+                                            oldval, rcu_dynticks_nesting));
                 return;
         }
-        RCU_TRACE(trace_rcu_dyntick("End", oldval));
+        RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
         if (!idle_cpu(smp_processor_id())) {
                 WARN_ON_ONCE(1);        /* must be idle task! */
                 RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
-                          oldval));
+                          oldval, rcu_dynticks_nesting));
                 ftrace_dump(DUMP_ALL);
         }
 }
@@ -127,7 +133,7 @@ void rcu_idle_exit(void)
         local_irq_save(flags);
         oldval = rcu_dynticks_nesting;
         WARN_ON_ONCE(oldval != 0);
-        rcu_dynticks_nesting = LLONG_MAX / 2;
+        rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
         rcu_idle_exit_common(oldval);
         local_irq_restore(flags);
 }
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 489b62a67d35..06e40dd53b23 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -196,7 +196,7 @@ void rcu_note_context_switch(int cpu)
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
-        .dynticks_nesting = LLONG_MAX / 2,
+        .dynticks_nesting = DYNTICK_TASK_NESTING,
         .dynticks = ATOMIC_INIT(1),
 };
 
@@ -348,17 +348,17 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
  * we really have entered idle, and must do the appropriate accounting.
  * The caller must have disabled interrupts.
  */
-static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
+static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
 {
         if (rdtp->dynticks_nesting) {
-                trace_rcu_dyntick("--=", rdtp->dynticks_nesting);
+                trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting);
                 return;
         }
-        trace_rcu_dyntick("Start", rdtp->dynticks_nesting);
+        trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting);
         if (!idle_cpu(smp_processor_id())) {
                 WARN_ON_ONCE(1);        /* must be idle task! */
                 trace_rcu_dyntick("Error on entry: not idle task",
-                                   rdtp->dynticks_nesting);
+                                   oldval, rdtp->dynticks_nesting);
                 ftrace_dump(DUMP_ALL);
         }
         /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
@@ -383,12 +383,14 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
 void rcu_idle_enter(void)
 {
         unsigned long flags;
+        long long oldval;
         struct rcu_dynticks *rdtp;
 
         local_irq_save(flags);
         rdtp = &__get_cpu_var(rcu_dynticks);
+        oldval = rdtp->dynticks_nesting;
         rdtp->dynticks_nesting = 0;
-        rcu_idle_enter_common(rdtp);
+        rcu_idle_enter_common(rdtp, oldval);
         local_irq_restore(flags);
 }
 
@@ -411,13 +413,15 @@ void rcu_idle_enter(void)
 void rcu_irq_exit(void)
 {
         unsigned long flags;
+        long long oldval;
         struct rcu_dynticks *rdtp;
 
         local_irq_save(flags);
         rdtp = &__get_cpu_var(rcu_dynticks);
+        oldval = rdtp->dynticks_nesting;
         rdtp->dynticks_nesting--;
         WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
-        rcu_idle_enter_common(rdtp);
+        rcu_idle_enter_common(rdtp, oldval);
         local_irq_restore(flags);
 }
 
@@ -431,7 +435,7 @@ void rcu_irq_exit(void)
 static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
 {
         if (oldval) {
-                trace_rcu_dyntick("++=", rdtp->dynticks_nesting);
+                trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting);
                 return;
         }
         smp_mb__before_atomic_inc();  /* Force ordering w/previous sojourn. */
@@ -439,10 +443,11 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
         /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
         smp_mb__after_atomic_inc();  /* See above. */
         WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
-        trace_rcu_dyntick("End", oldval);
+        trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
         if (!idle_cpu(smp_processor_id())) {
                 WARN_ON_ONCE(1);        /* must be idle task! */
-                trace_rcu_dyntick("Error on exit: not idle task", oldval);
+                trace_rcu_dyntick("Error on exit: not idle task",
+                                  oldval, rdtp->dynticks_nesting);
                 ftrace_dump(DUMP_ALL);
         }
 }
@@ -453,8 +458,8 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
  * Exit idle mode, in other words, -enter- the mode in which RCU
  * read-side critical sections can occur.
  *
- * We crowbar the ->dynticks_nesting field to LLONG_MAX/2 to allow for
- * the possibility of usermode upcalls messing up our count
+ * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
+ * allow for the possibility of usermode upcalls messing up our count
  * of interrupt nesting level during the busy period that is just
  * now starting.
  */
@@ -468,7 +473,7 @@ void rcu_idle_exit(void)
         rdtp = &__get_cpu_var(rcu_dynticks);
         oldval = rdtp->dynticks_nesting;
         WARN_ON_ONCE(oldval != 0);
-        rdtp->dynticks_nesting = LLONG_MAX / 2;
+        rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
         rcu_idle_exit_common(rdtp, oldval);
         local_irq_restore(flags);
 }
@@ -2012,7 +2017,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
                 rdp->nxttail[i] = &rdp->nxtlist;
         rdp->qlen = 0;
         rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
-        WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != LLONG_MAX / 2);
+        WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
         WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
         rdp->cpu = cpu;
         rdp->rsp = rsp;
@@ -2040,7 +2045,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
         rdp->qlen_last_fqs_check = 0;
         rdp->n_force_qs_snap = rsp->n_force_qs;
         rdp->blimit = blimit;
-        WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != LLONG_MAX / 2);
+        WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
         WARN_ON_ONCE((atomic_read(&rdp->dynticks->dynticks) & 0x1) != 1);
         raw_spin_unlock(&rnp->lock);            /* irqs remain disabled. */