On Tue, Apr 23, 2019 at 10:35:12PM +0200, Peter Zijlstra wrote: > On Tue, Apr 23, 2019 at 01:27:29PM -0700, Linus Torvalds wrote: > > On Tue, Apr 23, 2019 at 12:56 PM Peter Zijlstra <pet...@infradead.org> > > wrote: > > > > > > 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. > > > > That language may be a bit strong, or m,aybe the "implies it" might at > > least be extended on. > > > > It doesn't need to be "schedule()" per se, it can be any of the things > > that check if we _need_ to be scheduled. > > I'll try and word-smith that tomorrow, brain is fried. But yes, > something that ends up in schedule() 'soon'.
I've made that: Unless there is a call into schedule() in the immediate (deterministic) future, 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.
