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From: John Baldwin <jhb@FreeBSD.org>
To: Stephan Uphoff <ups@tree.com>
Date: Mon, 4 Oct 2004 13:21:45 -0400
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cc: Peter Holm <peter@holm.cc>
cc: Julian Elischer <julian@elischer.org>
cc: "freebsd-arch@freebsd.org" <freebsd-arch@FreeBSD.org>
Subject: Re: sched_switch (sched_4bsd) may be preempted
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On Friday 01 October 2004 01:55 am, Stephan Uphoff wrote:
> sched_switch (sched_4bsd) may be preempted in setrunqueue or slot_fill.
> This could be ugly.
> Wrapping it into a critical section and resetting TDP_OWEPREEMPT should
> work.
>
> Hand trimmed patch:
>
> RCS file: /cvsroot/src/sys/kern/sched_4bsd.c,v
> retrieving revision 1.65
> diff -u -r1.65 sched_4bsd.c
> --- sys/kern/sched_4bsd.c       16 Sep 2004 07:12:59 -0000      1.65
> +++ sys/kern/sched_4bsd.c       1 Oct 2004 05:35:28 -0000
> @@ -823,6 +823,7 @@
>                 TD_SET_CAN_RUN(td);
>         else {
>                 td->td_ksegrp->kg_avail_opennings++;
> +               critical_enter();
>                 if (TD_IS_RUNNING(td)) {
>                         /* Put us back on the run queue (kse and all).
> */
>                         setrunqueue(td, SRQ_OURSELF|SRQ_YIELDING);
> @@ -834,6 +835,8 @@
>                          */
>                         slot_fill(td->td_ksegrp);
>                 }
> +               critical_exit();
> +               td->td_pflags &= ~TDP_OWEPREEMPT;
>         }
>         if (newtd == NULL)
>                 newtd = choosethread();

I thought that SRQ_YIELDING turned preempting off already.

-- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org