alpha/85346: PREEMPTION causes unstability in Alpha4000 SMP kernel

[John Baldwin]

The following reply was made to PR alpha/85346; it has been noted by GNATS.

From: John Baldwin <jhb at FreeBSD.org>
To: bug-followup at FreeBSD.org,
 ken at alicorntech.com
Cc:  
Subject: Re: alpha/85346: PREEMPTION causes unstability in Alpha4000 SMP kernel
Date: Wed, 21 Sep 2005 15:17:01 -0400

 Hmm, I still don't run with PREEMPTION enabled on my DS20 on HEAD.  In my 
 experience I haven't gotten any panics, just hard locks when I have enabled 
 PREEMPTION and SMP on Alpha.  You can try testing this patch to see if it 
 helps things at all though:
 
 --- //depot/projects/smpng/sys/alpha/alpha/interrupt.c	2005/04/14 18:55:16
 +++ //depot/user/jhb/preemption/alpha/alpha/interrupt.c	2005/04/14 19:32:16
 @@ -427,6 +427,13 @@
  	atomic_add_long(i->cntp, 1);
  
  	/*
 +	 * It seems that we need to return from an interrupt back to PAL
 +	 * on the same CPU that received the interrupt, so pin the interrupted
 +	 * thread to the current CPU until we return from the interrupt.
 +	 */
 +	sched_pin();
 +
 +	/*
  	 * Handle a fast interrupt if there is no actual thread for this
  	 * interrupt by calling the handler directly without Giant.  Note
  	 * that this means that any fast interrupt handler must be MP safe.
 @@ -435,26 +442,18 @@
  	if ((ih->ih_flags & IH_FAST) != 0) {
  		critical_enter();
  		ih->ih_handler(ih->ih_argument);
 -		/* XXX */
 -		curthread->td_owepreempt = 0;
  		critical_exit();
 -		return;
 -	}
 +	} else {
 +		if (ithd->it_disable) {
 +			CTR1(KTR_INTR,
 +			    "alpha_dispatch_intr: disabling vector 0x%x",
 +			    i->vector);
 +			ithd->it_disable(ithd->it_vector);
 +		}
  
 -	if (ithd->it_disable) {
 -		CTR1(KTR_INTR,
 -		    "alpha_dispatch_intr: disabling vector 0x%x", i->vector);
 -		ithd->it_disable(ithd->it_vector);
 +		error = ithread_schedule(ithd);
 +		KASSERT(error == 0, ("got an impossible stray interrupt"));
  	}
 -
 -	/*
 -	 * It seems that we need to return from an interrupt back to PAL
 -	 * on the same CPU that received the interrupt, so pin the interrupted
 -	 * thread to the current CPU until we return from the interrupt.
 -	 */
 -	sched_pin();
 -	error = ithread_schedule(ithd);
 -	KASSERT(error == 0, ("got an impossible stray interrupt"));
  	sched_unpin();
  }
  
 --- //depot/projects/smpng/sys/kern/kern_thread.c	2005/05/27 14:58:46
 +++ //depot/user/jhb/preemption/kern/kern_thread.c	2005/05/27 19:03:12
 @@ -955,9 +957,11 @@
  	mtx_assert(&sched_lock, MA_OWNED);
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	if (!P_SHOULDSTOP(p)) {
 +		critical_enter();
  		while ((td = TAILQ_FIRST(&p->p_suspended))) {
  			thread_unsuspend_one(td);
  		}
 +		critical_exit();
  	} else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
  	    (p->p_numthreads == p->p_suspcount)) {
  		/*
 @@ -992,9 +996,11 @@
  	 * to continue however as this is a bad place to stop.
  	 */
  	if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
 +		critical_enter();
  		while ((td = TAILQ_FIRST(&p->p_suspended))) {
  			thread_unsuspend_one(td);
  		}
 +		critical_exit();
  	}
  	mtx_unlock_spin(&sched_lock);
  }
 --- //depot/projects/smpng/sys/kern/subr_sleepqueue.c	2005/09/15 19:40:43
 +++ //depot/user/jhb/preemption/kern/subr_sleepqueue.c	2005/09/15 20:09:55
 @@ -410,9 +410,10 @@
  	 * just return.
  	 */
  	if (td->td_sleepqueue != NULL) {
 -		MPASS(!TD_ON_SLEEPQ(td));
  		mtx_unlock_spin(&sc->sc_lock);
  		mtx_lock_spin(&sched_lock);
 +		MPASS(!TD_ON_SLEEPQ(td));
 +		MPASS(!TD_IS_SLEEPING(td));
  		return;
  	}
  
 --- //depot/projects/smpng/sys/vm/vm_glue.c	2005/05/27 14:58:46
 +++ //depot/user/jhb/preemption/vm/vm_glue.c	2005/05/27 19:03:12
 @@ -556,6 +556,7 @@
  			vm_thread_swapin(td);
  
  		PROC_LOCK(p);
 +		critical_enter();
  		mtx_lock_spin(&sched_lock);
  		p->p_sflag &= ~PS_SWAPPINGIN;
  		p->p_sflag |= PS_INMEM;
 @@ -570,6 +571,7 @@
  
  		/* Allow other threads to swap p out now. */
  		--p->p_lock;
 +		critical_exit();
  	}
  #endif /* NO_SWAPPING */
  }
 
 -- 
 John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
 "Power Users Use the Power to Serve"  =  http://www.FreeBSD.org