linux-kernel - [PATCH tip/core/rcu 3/4] rcu: Turn off tracing before dumping trace

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Message-Id: <1507153825-14136-3-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Wed,  4 Oct 2017 14:50:24 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 3/4] rcu: Turn off tracing before dumping trace

Currently, RCU allows tracing to continue when it automatically does
ftrace_dump() after detecting an error condition, which can result in
excessively large traces and lost trace events.  This commit therefore
does a tracing_off() before any of these ftrace_dump() calls.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/rcu.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index e4b43fef89f5..b8729eb09a5d 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -220,8 +220,10 @@ do { \
 	static atomic_t ___rfd_beenhere = ATOMIC_INIT(0); \
 	\
 	if (!atomic_read(&___rfd_beenhere) && \
-	    !atomic_xchg(&___rfd_beenhere, 1)) \
+	    !atomic_xchg(&___rfd_beenhere, 1)) { \
+		tracing_off(); \
 		ftrace_dump(oops_dump_mode); \
+	} \
 } while (0)
 
 void rcu_early_boot_tests(void);
-- 
2.5.2