[PATCH tip/core/rcu 4/4] rcu: Suppress RCU CPU stall warnings while dumping trace

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Currently, RCU emits Suppress RCU CPU stall warnings during its
automatically initiated ftrace_dump() calls after detecting an error
condition, which can result in excessively excessive console output
and lost trace events.  This commit therefore suppresses RCU CPU stall
warnings across any of these ftrace_dump() calls.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h    | 17 +++++++++++++++++
 kernel/rcu/update.c |  1 +
 2 files changed, 18 insertions(+)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index b8729eb09a5d..59c471de342a 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -203,6 +203,21 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 extern int rcu_cpu_stall_suppress;
 int rcu_jiffies_till_stall_check(void);
 
+#define rcu_ftrace_dump_stall_suppress() \
+do { \
+	if (!rcu_cpu_stall_suppress) \
+		rcu_cpu_stall_suppress = 3; \
+} while (0)
+
+#define rcu_ftrace_dump_stall_unsuppress() \
+do { \
+	if (rcu_cpu_stall_suppress == 3) \
+		rcu_cpu_stall_suppress = 0; \
+} while (0)
+
+#else /* #endif #ifdef CONFIG_RCU_STALL_COMMON */
+#define rcu_ftrace_dump_stall_suppress()
+#define rcu_ftrace_dump_stall_unsuppress()
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 
 /*
@@ -222,7 +237,9 @@ do { \
 	if (!atomic_read(&___rfd_beenhere) && \
 	    !atomic_xchg(&___rfd_beenhere, 1)) { \
 		tracing_off(); \
+		rcu_ftrace_dump_stall_suppress(); \
 		ftrace_dump(oops_dump_mode); \
+		rcu_ftrace_dump_stall_unsuppress(); \
 	} \
 } while (0)
 
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 5033b66d2753..3dc8efb16dc7 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -494,6 +494,7 @@ EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 #endif
 
 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
+EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
 static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 
 module_param(rcu_cpu_stall_suppress, int, 0644);
-- 
2.5.2