Author: fabient
Date: Thu Mar 31 13:59:47 2011
New Revision: 220198
URL: http://svn.freebsd.org/changeset/base/220198
Log:
Clearing the flag when preempting will let the preempted thread run
too much time. This can finish in a scheduler deadlock with ping-pong
between two threads.
One sample of this is:
- device lapic (to have a preemption point on critical_exit())
- options DEVICE_POLLING with HZ>1499 (to have lapic freq = hardclock freq)
- running a cpu intensive task (that does not enter the kernel)
- only one CPU on SMP or no SMP.
As requested by jhb@ 4BSD have received the same type of fix instead of
propagating the flag to the new thread.
Reviewed by: jhb, jeff
MFC after: 1 month
Modified:
head/sys/kern/sched_4bsd.c
head/sys/kern/sched_ule.c
Modified: head/sys/kern/sched_4bsd.c
==============================================================================
--- head/sys/kern/sched_4bsd.c Thu Mar 31 13:36:31 2011 (r220197)
+++ head/sys/kern/sched_4bsd.c Thu Mar 31 13:59:47 2011 (r220198)
@@ -940,13 +940,9 @@ sched_switch(struct thread *td, struct t
if ((td->td_flags & TDF_NOLOAD) == 0)
sched_load_rem();
- if (newtd) {
- MPASS(newtd->td_lock == &sched_lock);
- newtd->td_flags |= (td->td_flags & TDF_NEEDRESCHED);
- }
-
td->td_lastcpu = td->td_oncpu;
- td->td_flags &= ~TDF_NEEDRESCHED;
+ if (!(flags & SW_PREEMPT))
+ td->td_flags &= ~TDF_NEEDRESCHED;
td->td_owepreempt = 0;
td->td_oncpu = NOCPU;
Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c Thu Mar 31 13:36:31 2011 (r220197)
+++ head/sys/kern/sched_ule.c Thu Mar 31 13:59:47 2011 (r220198)
@@ -1783,7 +1783,8 @@ sched_switch(struct thread *td, struct t
ts->ts_rltick = ticks;
td->td_lastcpu = td->td_oncpu;
td->td_oncpu = NOCPU;
- td->td_flags &= ~TDF_NEEDRESCHED;
+ if (!(flags & SW_PREEMPT))
+ td->td_flags &= ~TDF_NEEDRESCHED;
td->td_owepreempt = 0;
tdq->tdq_switchcnt++;
/*
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