From: Peter Zijlstra peterz@infradead.org

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....

Cc: Waiman Long longman@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Ingo Molnar mingo@redhat.com Cc: Will Deacon will.deacon@arm.com Cc: Thomas Gleixner tglx@linutronix.de Cc: the arch/x86 maintainers x86@kernel.org Cc: Davidlohr Bueso dave@stgolabs.net Cc: Tim Chen tim.c.chen@linux.intel.com Cc: huang ying huang.ying.caritas@gmail.com Cc: Roman Gushchin guro@fb.com Cc: Alexei Starovoitov ast@kernel.org Cc: Daniel Borkmann daniel@iogearbox.net Cc: stable@vger.kernel.org Fixes: 2c2d7329d8af ("tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time_stamp()") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.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; }