Messages in this thread Patch in this message | | | Date | Tue, 23 Apr 2019 22:03:18 +0200 | From | Peter Zijlstra <> | Subject | [PATCH] trace: Fix preempt_enable_no_resched() abuse |
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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 <rostedt@goodmis.org> Fixes: 37886f6a9f62 ("ring-buffer: add api to allow a tracer to change clock source") Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.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; }
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