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>

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 172620a92b1a86afaea48167ca8a85222a8f33e3..c29fb2f559090792cfa3531bf7b9f9024c529084 100644 (file)
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -246,21 +246,24 @@ TRACE_EVENT(rcu_fqs,
  */
 TRACE_EVENT(rcu_dyntick,
 
-       TP_PROTO(char *polarity, int nesting),
+       TP_PROTO(char *polarity, long long oldnesting, long long newnesting),
 
-       TP_ARGS(polarity, nesting),
+       TP_ARGS(polarity, oldnesting, newnesting),
 
        TP_STRUCT__entry(
                __field(char *, polarity)
-               __field(int, nesting)
+               __field(long long, oldnesting)
+               __field(long long, newnesting)
        ),
 
        TP_fast_assign(
                __entry->polarity = polarity;
-               __entry->nesting = nesting;
+               __entry->oldnesting = oldnesting;
+               __entry->newnesting = newnesting;
        ),
 
-       TP_printk("%s %d", __entry->polarity, __entry->nesting)
+       TP_printk("%s %llx %llx", __entry->polarity,
+                 __entry->oldnesting, __entry->newnesting)
 );
 
 /*
@@ -470,7 +473,7 @@ TRACE_EVENT(rcu_torture_read,
 #define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0)
 #define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, grplo, grphi, gp_tasks) do { } while (0)
 #define trace_rcu_fqs(rcuname, gpnum, cpu, qsevent) do { } while (0)
-#define trace_rcu_dyntick(polarity, nesting) do { } while (0)
+#define trace_rcu_dyntick(polarity, oldnesting, newnesting) do { } while (0)
 #define trace_rcu_callback(rcuname, rhp, qlen) do { } while (0)
 #define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen) do { } while (0)
 #define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0)

diff --git a/kernel/rcu.h b/kernel/rcu.h
index f600868d550dc1764f7541f3cf87c14589f007f7..aa88baab5f78a715bfca877a0dee9a81354195e2 100644 (file)
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -29,6 +29,13 @@
 #define RCU_TRACE(stmt)
 #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

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index b4e0b498176869ba0def3ff0bb2ef0120cfe50c4..9b9bdf666fb5027a061ca50cd70c842266bb92c5 100644 (file)
--- 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 489b62a67d359aa23e3c58e0337ccb32290491cc..06e40dd53b23847a8aadadd966e26db6a39e76aa 100644 (file)
--- 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. */