linux-kernel - [PATCH 3.16 112/157] trace: Fix preempt_enable_no

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Message-ID: <lsq.1565469607.775611502@decadent.org.uk>
Date:   Sat, 10 Aug 2019 21:40:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Roman Gushchin" <guro@...com>,
        "Will Deacon" <will.deacon@....com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "huang ying" <huang.ying.caritas@...il.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Alexei Starovoitov" <ast@...nel.org>,
        "Davidlohr Bueso" <dave@...olabs.net>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "Tim Chen" <tim.c.chen@...ux.intel.com>,
        "Waiman Long" <longman@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 112/157] trace: Fix preempt_enable_no_resched() abuse

3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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>
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: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -729,7 +729,7 @@ 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;
 }