On Tuesday, May 17, 2011 12:20:40 pm Max Laier wrote: > On 05/17/2011 05:16 AM, John Baldwin wrote: > ... > > Index: kern/kern_switch.c > > =================================================================== > > --- kern/kern_switch.c (revision 221536) > > +++ kern/kern_switch.c (working copy) > > @@ -192,15 +192,22 @@ > > critical_exit(void) > > { > > struct thread *td; > > - int flags; > > + int flags, owepreempt; > > > > td = curthread; > > KASSERT(td->td_critnest != 0, > > ("critical_exit: td_critnest == 0")); > > > > if (td->td_critnest == 1) { > > + owepreempt = td->td_owepreempt; > > + td->td_owepreempt = 0; > > + /* > > + * XXX: Should move compiler_memory_barrier() from > > + * rmlock to a header. > > + */ > > XXX: If we get an interrupt at this point and td_owepreempt was zero, > the new interrupt will re-set it, because td_critnest is still non-zero. > > So we still end up with a thread that is leaking an owepreempt *and* > lose a preemption.
I don't see how this can still leak owepreempt. The nested interrupt should do nothing (except for possibly set owepreempt) until td_critnest is 0. However, we can certainly lose preemptions. I wonder if we can abuse the high bit of td_critnest for the owepreempt flag so it is all stored in one cookie. We only set owepreempt while holding thread_lock() (so interrupts are disabled), so I think we would be ok and not need atomic ops. Hmm, actually, the top-half code would have to use atomic ops. Nuts. Let me think some more. -- John Baldwin _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"