From 586cb6ec77ccb471dbb115817a9e39f29dd95ac2 Mon Sep 17 00:00:00 2001 From: Fabien Thomas Date: Thu, 31 Mar 2011 13:59:47 +0000 Subject: [PATCH] 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 --- sys/kern/sched_4bsd.c | 8 ++------ sys/kern/sched_ule.c | 3 ++- 2 files changed, 4 insertions(+), 7 deletions(-) diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c index f7025b0d96e8..c96d7b54ba7d 100644 --- a/sys/kern/sched_4bsd.c +++ b/sys/kern/sched_4bsd.c @@ -940,13 +940,9 @@ sched_switch(struct thread *td, struct thread *newtd, int flags) 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; diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c index c1bb98f7cd9e..ac18e778ae28 100644 --- a/sys/kern/sched_ule.c +++ b/sys/kern/sched_ule.c @@ -1783,7 +1783,8 @@ sched_switch(struct thread *td, struct thread *newtd, int flags) 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++; /*