Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU changes from Ingo Molnar:
 "SRCU changes:

   - These include debugging aids, updates that move towards the goal of
     permitting srcu_read_lock() and srcu_read_unlock() to be used from
     idle and offline CPUs, and a few small fixes.

  Changes to rcutorture and to RCU documentation:

   - Posted to LKML at https://lkml.org/lkml/2013/1/26/188

  Enhancements to uniprocessor handling in tiny RCU:

   - Posted to LKML at https://lkml.org/lkml/2013/1/27/2

  Tag RCU callbacks with grace-period number to simplify callback
  advancement:

   - Posted to LKML at https://lkml.org/lkml/2013/1/26/203

  Miscellaneous fixes:

   - Posted to LKML at https://lkml.org/lkml/2013/1/26/204"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (27 commits)
  srcu: use ACCESS_ONCE() to access sp->completed in srcu_read_lock()
  srcu: Update synchronize_srcu_expedited()'s comments
  srcu: Update synchronize_srcu()'s comments
  srcu: Remove checks preventing idle CPUs from calling srcu_read_lock()
  srcu: Remove checks preventing offline CPUs from calling srcu_read_lock()
  srcu: Simple cleanup for cleanup_srcu_struct()
  srcu: Add might_sleep() annotation to synchronize_srcu()
  srcu: Simplify __srcu_read_unlock() via this_cpu_dec()
  rcu: Allow rcutorture to be built at low optimization levels
  rcu: Make rcutorture's shuffler task shuffle recently added tasks
  rcu: Allow TREE_PREEMPT_RCU on UP systems
  rcu: Provide RCU CPU stall warnings for tiny RCU
  context_tracking: Add comments on interface and internals
  rcu: Remove obsolete Kconfig option from comment
  rcu: Remove unused code originally used for context tracking
  rcu: Consolidate debugging Kconfig options
  rcu: Correct 'optimized' to 'optimize' in header comment
  rcu: Trace callback acceleration
  rcu: Tag callback lists with corresponding grace-period number
  rcutorture: Don't compare ptr with 0
  ...

1 files changed, 56 insertions, 0 deletions

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index f85016a2309..8a233002fae 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -33,6 +33,9 @@ struct rcu_ctrlblk {
 	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
 	struct rcu_head **curtail;	/* ->next pointer of last CB. */
 	RCU_TRACE(long qlen);		/* Number of pending CBs. */
+	RCU_TRACE(unsigned long gp_start); /* Start time for stalls. */
+	RCU_TRACE(unsigned long ticks_this_gp); /* Statistic for stalls. */
+	RCU_TRACE(unsigned long jiffies_stall); /* Jiffies at next stall. */
 	RCU_TRACE(char *name);		/* Name of RCU type. */
 };
 
@@ -54,6 +57,51 @@ int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+#ifdef CONFIG_RCU_TRACE
+
+static void check_cpu_stall(struct rcu_ctrlblk *rcp)
+{
+	unsigned long j;
+	unsigned long js;
+
+	if (rcu_cpu_stall_suppress)
+		return;
+	rcp->ticks_this_gp++;
+	j = jiffies;
+	js = rcp->jiffies_stall;
+	if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
+		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
+		       rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
+		       jiffies - rcp->gp_start, rcp->qlen);
+		dump_stack();
+	}
+	if (*rcp->curtail && ULONG_CMP_GE(j, js))
+		rcp->jiffies_stall = jiffies +
+			3 * rcu_jiffies_till_stall_check() + 3;
+	else if (ULONG_CMP_GE(j, js))
+		rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+}
+
+static void check_cpu_stall_preempt(void);
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
+static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
+{
+#ifdef CONFIG_RCU_TRACE
+	rcp->ticks_this_gp = 0;
+	rcp->gp_start = jiffies;
+	rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+#endif /* #ifdef CONFIG_RCU_TRACE */
+}
+
+static void check_cpu_stalls(void)
+{
+	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
+	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
+	RCU_TRACE(check_cpu_stall_preempt());
+}
+
 #ifdef CONFIG_TINY_PREEMPT_RCU
 
 #include <linux/delay.h>
@@ -448,6 +496,7 @@ static void rcu_preempt_start_gp(void)
 		/* Official start of GP. */
 		rcu_preempt_ctrlblk.gpnum++;
 		RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
+		reset_cpu_stall_ticks(&rcu_preempt_ctrlblk.rcb);
 
 		/* Any blocked RCU readers block new GP. */
 		if (rcu_preempt_blocked_readers_any())
@@ -1054,4 +1103,11 @@ MODULE_AUTHOR("Paul E. McKenney");
 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
 MODULE_LICENSE("GPL");
 
+static void check_cpu_stall_preempt(void)
+{
+#ifdef CONFIG_TINY_PREEMPT_RCU
+	check_cpu_stall(&rcu_preempt_ctrlblk.rcb);
+#endif /* #ifdef CONFIG_TINY_PREEMPT_RCU */
+}
+
 #endif /* #ifdef CONFIG_RCU_TRACE */