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Date:   Tue, 30 Apr 2019 13:38:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Waiman Long <longman@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>,
        Roman Gushchin <guro@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Subject: [PATCH 4.9 05/41] trace: Fix preempt_enable_no_resched() abuse

From: Peter Zijlstra <peterz@...radead.org>

commit d6097c9e4454adf1f8f2c9547c2fa6060d55d952 upstream.

Unless the very next line is schedule(), or implies it, 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.

Link: http://lkml.kernel.org/r/20190423200318.GY14281@hirez.programming.kicks-ass.net

Cc: Waiman Long <longman@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will.deacon@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: the arch/x86 maintainers <x86@...nel.org>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: huang ying <huang.ying.caritas@...il.com>
Cc: Roman Gushchin <guro@...com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: stable@...r.kernel.org
Fixes: 2c2d7329d8af ("tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time_stamp()")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/trace/ring_buffer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -701,7 +701,7 @@ u64 ring_buffer_time_stamp(struct ring_b
 
 	preempt_disable_notrace();
 	time = rb_time_stamp(buffer);
-	preempt_enable_no_resched_notrace();
+	preempt_enable_notrace();
 
 	return time;
 }


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