---

yaml
---
r: 288583
b: refs/heads/master
c: 29e37d8
h: refs/heads/master
i:
  288581: 5623c89
  288579: 58166c4
  288575: 3bcbab8
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: ce5df97be530e4746bf9a4ac14589a1cfdfd8efc
+refs/heads/master: 29e37d814188ac8d60f2120583704d3ef6d634b4

trunk/kernel/rcu.h

@@ -33,8 +33,27 @@
  * Process-level increment to ->dynticks_nesting field.  This allows for
  * architectures that use half-interrupts and half-exceptions from
  * process context.
+ *
+ * DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
+ * that counts the number of process-based reasons why RCU cannot
+ * consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
+ * is the value used to increment or decrement this field.
+ *
+ * The rest of the bits could in principle be used to count interrupts,
+ * but this would mean that a negative-one value in the interrupt
+ * field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
+ * We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
+ * that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
+ * The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
+ * initial exit from idle.
  */
-#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1)
+#define DYNTICK_TASK_NEST_WIDTH 7
+#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
+#define DYNTICK_TASK_NEST_MASK  (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
+#define DYNTICK_TASK_FLAG	   ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
+#define DYNTICK_TASK_MASK	   ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
+#define DYNTICK_TASK_EXIT_IDLE	   (DYNTICK_TASK_NEST_VALUE + \
+				    DYNTICK_TASK_FLAG)
 
 /*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally

trunk/kernel/rcutiny.c

@@ -53,7 +53,7 @@ static void __call_rcu(struct rcu_head *head,
 
 #include "rcutiny_plugin.h"
 
-static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
+static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 
 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
 static void rcu_idle_enter_common(long long oldval)
@@ -88,7 +88,12 @@ void rcu_idle_enter(void)
 
 	local_irq_save(flags);
 	oldval = rcu_dynticks_nesting;
-	rcu_dynticks_nesting = 0;
+	WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
+	if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
+	    DYNTICK_TASK_NEST_VALUE)
+		rcu_dynticks_nesting = 0;
+	else
+		rcu_dynticks_nesting  -= DYNTICK_TASK_NEST_VALUE;
 	rcu_idle_enter_common(oldval);
 	local_irq_restore(flags);
 }
@@ -140,8 +145,11 @@ void rcu_idle_exit(void)
 
 	local_irq_save(flags);
 	oldval = rcu_dynticks_nesting;
-	WARN_ON_ONCE(oldval != 0);
-	rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
+	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
+	if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
+		rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
+	else
+		rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_idle_exit_common(oldval);
 	local_irq_restore(flags);
 }

trunk/kernel/rcutree.c

@@ -198,7 +198,7 @@ void rcu_note_context_switch(int cpu)
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
-	.dynticks_nesting = DYNTICK_TASK_NESTING,
+	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
 	.dynticks = ATOMIC_INIT(1),
 };
 
@@ -394,7 +394,11 @@ void rcu_idle_enter(void)
 	local_irq_save(flags);
 	rdtp = &__get_cpu_var(rcu_dynticks);
 	oldval = rdtp->dynticks_nesting;
-	rdtp->dynticks_nesting = 0;
+	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
+	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
+		rdtp->dynticks_nesting = 0;
+	else
+		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
 	rcu_idle_enter_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
@@ -467,7 +471,7 @@ 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 DYNTICK_TASK_NESTING to
+ * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST 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.
@@ -481,8 +485,11 @@ void rcu_idle_exit(void)
 	local_irq_save(flags);
 	rdtp = &__get_cpu_var(rcu_dynticks);
 	oldval = rdtp->dynticks_nesting;
-	WARN_ON_ONCE(oldval != 0);
-	rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
+	WARN_ON_ONCE(oldval < 0);
+	if (oldval & DYNTICK_TASK_NEST_MASK)
+		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
+	else
+		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_idle_exit_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
@@ -2253,7 +2260,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
 	rdp->qlen_lazy = 0;
 	rdp->qlen = 0;
 	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
-	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
+	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
 	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
 	rdp->cpu = cpu;
 	rdp->rsp = rsp;
@@ -2281,7 +2288,7 @@ 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;
-	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_NESTING;
+	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	atomic_set(&rdp->dynticks->dynticks,
 		   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
 	rcu_prepare_for_idle_init(cpu);