[tip:sched/core] trace: Fix preempt_enable_no_resched() abuse

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  e8bd5814989b994cf1b0cb179e1c777e40c0f02c
Gitweb:     https://git.kernel.org/tip/e8bd5814989b994cf1b0cb179e1c777e40c0f02c
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 23 Apr 2019 22:03:18 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 29 Apr 2019 08:27:09 +0200

trace: Fix preempt_enable_no_resched() abuse

Unless there is a call into schedule() in the immediate
(deterministic) future, one must not use preempt_enable_no_resched().
It can cause a preemption to go missing and thereby cause arbitrary
delays, breaking the PREEMPT=y invariant.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Fixes: 2c2d7329d8af ("tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time_stamp()")
Link: https://lkml.kernel.org/r/20190423200318.GY14281@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 41b6f96e5366..4ee8d8aa3d0f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -762,7 +762,7 @@ u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
 
 	preempt_disable_notrace();
 	time = rb_time_stamp(buffer);
-	preempt_enable_no_resched_notrace();
+	preempt_enable_notrace();
 
 	return time;
 }