releases/4.4.180/trace-fix-preempt_enable_no_resched-abuse.patch

   1 From d6097c9e4454adf1f8f2c9547c2fa6060d55d952 Mon Sep 17 00:00:00 2001
   2 From: Peter Zijlstra <peterz@infradead.org>
   3 Date: Tue, 23 Apr 2019 22:03:18 +0200
   4 Subject: trace: Fix preempt_enable_no_resched() abuse
   5
   6 From: Peter Zijlstra <peterz@infradead.org>
   7
   8 commit d6097c9e4454adf1f8f2c9547c2fa6060d55d952 upstream.
   9
  10 Unless the very next line is schedule(), or implies it, one must not use
  11 preempt_enable_no_resched(). It can cause a preemption to go missing and
  12 thereby cause arbitrary delays, breaking the PREEMPT=y invariant.
  13
  14 Link: http://lkml.kernel.org/r/20190423200318.GY14281@hirez.programming.kicks-ass.net
  15
  16 Cc: Waiman Long <longman@redhat.com>
  17 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  18 Cc: Ingo Molnar <mingo@redhat.com>
  19 Cc: Will Deacon <will.deacon@arm.com>
  20 Cc: Thomas Gleixner <tglx@linutronix.de>
  21 Cc: the arch/x86 maintainers <x86@kernel.org>
  22 Cc: Davidlohr Bueso <dave@stgolabs.net>
  23 Cc: Tim Chen <tim.c.chen@linux.intel.com>
  24 Cc: huang ying <huang.ying.caritas@gmail.com>
  25 Cc: Roman Gushchin <guro@fb.com>
  26 Cc: Alexei Starovoitov <ast@kernel.org>
  27 Cc: Daniel Borkmann <daniel@iogearbox.net>
  28 Cc: stable@vger.kernel.org
  29 Fixes: 2c2d7329d8af ("tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time_stamp()")
  30 Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
  31 Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
  32 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  33
  34 ---
  35  kernel/trace/ring_buffer.c |    2 +-
  36  1 file changed, 1 insertion(+), 1 deletion(-)
  37
  38 --- a/kernel/trace/ring_buffer.c
  39 +++ b/kernel/trace/ring_buffer.c
  40 @@ -701,7 +701,7 @@ u64 ring_buffer_time_stamp(struct ring_b
  41
  42         preempt_disable_notrace();
  43         time = rb_time_stamp(buffer);
  44 -       preempt_enable_no_resched_notrace();
  45 +       preempt_enable_notrace();
  46
  47         return time;
  48  }