Date: Fri, 6 May 2011 14:11:20 +0000 (UTC) From: Fabien Thomas <fabient@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org Subject: svn commit: r221532 - stable/7/sys/kern Message-ID: <201105061411.p46EBKiA051601@svn.freebsd.org>
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Author: fabient Date: Fri May 6 14:11:20 2011 New Revision: 221532 URL: http://svn.freebsd.org/changeset/base/221532 Log: MFC r220198: 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. Modified: stable/7/sys/kern/sched_4bsd.c stable/7/sys/kern/sched_ule.c Directory Properties: stable/7/sys/ (props changed) stable/7/sys/cddl/contrib/opensolaris/ (props changed) stable/7/sys/contrib/dev/acpica/ (props changed) stable/7/sys/contrib/pf/ (props changed) Modified: stable/7/sys/kern/sched_4bsd.c ============================================================================== --- stable/7/sys/kern/sched_4bsd.c Fri May 6 14:11:01 2011 (r221531) +++ stable/7/sys/kern/sched_4bsd.c Fri May 6 14:11:20 2011 (r221532) @@ -848,13 +848,9 @@ sched_switch(struct thread *td, struct t if ((p->p_flag & P_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: stable/7/sys/kern/sched_ule.c ============================================================================== --- stable/7/sys/kern/sched_ule.c Fri May 6 14:11:01 2011 (r221531) +++ stable/7/sys/kern/sched_ule.c Fri May 6 14:11:20 2011 (r221532) @@ -1879,7 +1879,8 @@ sched_switch(struct thread *td, struct t #endif 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; /* * The lock pointer in an idle thread should never change. Reset it
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