Date: Mon, 04 Oct 2004 11:38:46 -0700 From: Julian Elischer <julian@elischer.org> To: John Baldwin <jhb@freebsd.org> Cc: Stephan Uphoff <ups@tree.com> Subject: Re: sched_switch (sched_4bsd) may be preempted Message-ID: <416198B6.4030801@elischer.org> In-Reply-To: <200410041321.45142.jhb@FreeBSD.org> References: <1096610130.21577.219.camel@palm.tree.com> <200410041321.45142.jhb@FreeBSD.org>
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John Baldwin wrote:
>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.
>
>
well, that was the intention.. I wonder if there can be more nesting than we expect?
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