linux-kernel - [tip:x86/urgent] x86: Use preempt_disable_notrace() in cycles_2

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Message-ID: <tip-569d6557ab957d6ae7e97a46ae669174be4189e6@git.kernel.org>
Date:	Mon, 10 Feb 2014 05:28:43 -0800
From:	tip-bot for Steven Rostedt <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, rostedt@...dmis.org,
	peterz@...radead.org, tglx@...utronix.de
Subject: [tip:x86/urgent] x86: Use preempt_disable_notrace()
  in cycles_2_ns()

Commit-ID:  569d6557ab957d6ae7e97a46ae669174be4189e6
Gitweb:     http://git.kernel.org/tip/569d6557ab957d6ae7e97a46ae669174be4189e6
Author:     Steven Rostedt <rostedt@...dmis.org>
AuthorDate: Tue, 4 Feb 2014 14:13:15 -0500
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sun, 9 Feb 2014 13:09:08 +0100

x86: Use preempt_disable_notrace() in cycles_2_ns()

When debug preempt is enabled, preempt_disable() can be traced by
function and function graph tracing.

There's a place in the function graph tracer that calls trace_clock()
which eventually calls cycles_2_ns() outside of the recursion
protection. When cycles_2_ns() calls preempt_disable() it gets traced
and the graph tracer will go into a recursive loop causing a crash or
worse, a triple fault.

Simple fix is to use preempt_disable_notrace() in cycles_2_ns, which
makes sense because the preempt_disable() tracing may use that code
too, and it tracing it, even with recursion protection is rather
pointless.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/20140204141315.2a968a72@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/tsc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 19e5adb..acb3b60 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -209,7 +209,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 	 * dance when its actually needed.
 	 */
 
-	preempt_disable();
+	preempt_disable_notrace();
 	data = this_cpu_read(cyc2ns.head);
 	tail = this_cpu_read(cyc2ns.tail);
 
@@ -229,7 +229,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 		if (!--data->__count)
 			this_cpu_write(cyc2ns.tail, data);
 	}
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return ns;
 }
--
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