On Tue, Apr 23, 2019 at 09:55:59PM +0200, Peter Zijlstra wrote: > On Tue, Apr 23, 2019 at 03:41:32PM -0400, Waiman Long wrote:
> > I saw a number of instances of > > preempt_enable_no_resched() without right next a schedule(). > > Look more closely.. and let me know, if true, those are bugs that need > fixing. > > Argghhh.. BPF... /me shakes head, Steve... --- Subject: trace: Fix preempt_enable_no_resched() abuse 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. Cc: Steven Rostedt <[email protected]> Fixes: 37886f6a9f62 ("ring-buffer: add api to allow a tracer to change clock source") Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- 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; }
