Date:	Wed, 11 Aug 2010 09:32:15 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC PATCH 2/2] rcu,debug_core: allow the kernel debugger to
 reset the rcu stall timer

On Wed, Aug 11, 2010 at 09:07:05AM -0500, Jason Wessel wrote:
> On 08/10/2010 11:01 PM, Paul E. McKenney wrote:
> > On Mon, Aug 09, 2010 at 12:01:42PM -0700, Paul E. McKenney wrote:
> > 
> > Here is an initial patch.  Untested, probably doesn't even compile.
> > It is against my -rcu tree:
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/testing
> > 
> > Thoughts?
> 
> Paul, I tried this out and code wise it looks fine to me. I performed
> a compile and regression test with the various kernel config options
> to cover this new code.

Very good, I have added your Tested-by.

> Thanks for fixing the rcu_preempt case that my original patch missed.
> Because you used the same name for the function it was an easy drop in
> replacement.  :-)

No problem!  As to keeping your name, don't worry, I won't let that
happen again.  ;-)

> Signed-off-by: Jason Wessel <jason.wessel@...driver.com>

Ah, yes -- I started from your patch, so I should have kept your
Signed-off-by.  My apologies for failing to do so.  I have added it
back in, please see below.

I have this commit queued for 2.6.37.

							Thanx, Paul

commit e7732983e72865c30754b8be70482e6e8842a945
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date:   Tue Aug 10 14:28:53 2010 -0700

    rcu: permit suppressing current grace period's CPU stall warnings
    
    When using a kernel debugger, a long sojourn in the debugger can get
    you lots of RCU CPU stall warnings once you resume.  This might not be
    helpful, especially if you are using the system console.  This patch
    therefore allows RCU CPU stall warnings to be suppressed, but only for
    the duration of the current set of grace periods.
    
    This differs from Jason's original patch in that it adds support for
    tiny RCU and preemptible RCU, and uses a slightly different method for
    suppressing the RCU CPU stall warning messages.
    
    Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
    Tested-by: Jason Wessel <jason.wessel@...driver.com>

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4cc5eba..3fa1797 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -178,6 +178,10 @@ static inline void rcu_sched_force_quiescent_state(void)
 {
 }
 
+static inline void rcu_cpu_stall_reset(void)
+{
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 extern int rcu_scheduler_active __read_mostly;
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index c13b85d..0726809 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -36,6 +36,7 @@ extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
 extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu);
+extern void rcu_cpu_stall_reset(void);
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
 
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ff21411..42140a8 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -565,6 +565,22 @@ static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 	return NOTIFY_DONE;
 }
 
+/**
+ * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
+ *
+ * Set the stall-warning timeout way off into the future, thus preventing
+ * any RCU CPU stall-warning messages from appearing in the current set of
+ * RCU grace periods.
+ *
+ * The caller must disable hard irqs.
+ */
+void rcu_cpu_stall_reset(void)
+{
+	rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+	rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+	rcu_preempt_stall_reset();
+}
+
 static struct notifier_block rcu_panic_block = {
 	.notifier_call = rcu_panic,
 };
@@ -584,6 +600,10 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 {
 }
 
+void rcu_cpu_stall_reset(void)
+{
+}
+
 static void __init check_cpu_stall_init(void)
 {
 }
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index bb4d086..7abd439 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -372,6 +372,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
 static void rcu_print_detail_task_stall(struct rcu_state *rsp);
 static void rcu_print_task_stall(struct rcu_node *rnp);
+static void rcu_preempt_stall_reset(void);
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
 #ifdef CONFIG_HOTPLUG_CPU
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 63bb771..561410f 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -417,6 +417,16 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 	}
 }
 
+/*
+ * Suppress preemptible RCU's CPU stall warnings by pushing the
+ * time of the next stall-warning message comfortably far into the
+ * future.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+	rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+}
+
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
 /*
@@ -867,6 +877,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 {
 }
 
+/*
+ * Because preemptible RCU does not exist, there is no need to suppress
+ * its CPU stall warnings.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+}
+
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
 /*
--
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