Commit 10/14 of sched_lock decomposition.

- Use sched_throw() rather than replicating the same cpu_throw() code for
   each architecture.  This also allows the scheduler to use any locking it
   may want to.
 - Use the thread_lock() rather than sched_lock when preempting.
 - The scheduler lock is not required to synchronize release_aps.

Tested by:      kris, current@
Tested on:      i386, amd64, ULE, 4BSD, libthr, libkse, PREEMPTION, etc.
Discussed with: kris, attilio, kmacy, jhb, julian, bde (small parts each)

sys/amd64/amd64/mp_machdep.c

@@ -46,6 +46,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/mutex.h>
 #include <sys/pcpu.h>
 #include <sys/proc.h>
+#include <sys/sched.h>
 #include <sys/smp.h>
 #include <sys/sysctl.h>
 
@@ -590,25 +591,7 @@ init_secondary(void)
 	while (smp_started == 0)
 		ia32_pause();
 
-	/* ok, now grab sched_lock and enter the scheduler */
-	mtx_lock_spin(&sched_lock);
-
-	/*
-	 * Correct spinlock nesting.  The idle thread context that we are
-	 * borrowing was created so that it would start out with a single
-	 * spin lock (sched_lock) held in fork_trampoline().  Since we've
-	 * explicitly acquired locks in this function, the nesting count
-	 * is now 2 rather than 1.  Since we are nested, calling
-	 * spinlock_exit() will simply adjust the counts without allowing
-	 * spin lock using code to interrupt us.
-	 */
-	spinlock_exit();
-	KASSERT(curthread->td_md.md_spinlock_count == 1, ("invalid count"));
-
-	PCPU_SET(switchtime, cpu_ticks());
-	PCPU_SET(switchticks, ticks);
-
-	cpu_throw(NULL, choosethread());	/* doesn't return */
+	sched_throw(NULL);
 
 	panic("scheduler returned us to %s", __func__);
 	/* NOTREACHED */
@@ -988,12 +971,12 @@ ipi_bitmap_handler(struct trapframe frame)
 
 	if (ipi_bitmap & (1 << IPI_PREEMPT)) {
 		struct thread *running_thread = curthread;
-		mtx_lock_spin(&sched_lock);
+		thread_lock(running_thread);
 		if (running_thread->td_critnest > 1) 
 			running_thread->td_owepreempt = 1;
 		else 		
 			mi_switch(SW_INVOL | SW_PREEMPT, NULL);
-		mtx_unlock_spin(&sched_lock);
+		thread_unlock(running_thread);
 	}
 
 	/* Nothing to do for AST */
@@ -1177,11 +1160,9 @@ release_aps(void *dummy __unused)
 
 	if (mp_ncpus == 1) 
 		return;
-	mtx_lock_spin(&sched_lock);
 	atomic_store_rel_int(&aps_ready, 1);
 	while (smp_started == 0)
 		ia32_pause();
-	mtx_unlock_spin(&sched_lock);
 }
 SYSINIT(start_aps, SI_SUB_SMP, SI_ORDER_FIRST, release_aps, NULL);
 

sys/i386/i386/mp_machdep.c

@@ -61,6 +61,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/mutex.h>
 #include <sys/pcpu.h>
 #include <sys/proc.h>
+#include <sys/sched.h>
 #include <sys/smp.h>
 #include <sys/sysctl.h>
 
@@ -642,25 +643,8 @@ init_secondary(void)
 	while (smp_started == 0)
 		ia32_pause();
 
-	/* ok, now grab sched_lock and enter the scheduler */
-	mtx_lock_spin(&sched_lock);
-
-	/*
-	 * Correct spinlock nesting.  The idle thread context that we are
-	 * borrowing was created so that it would start out with a single
-	 * spin lock (sched_lock) held in fork_trampoline().  Since we've
-	 * explicitly acquired locks in this function, the nesting count
-	 * is now 2 rather than 1.  Since we are nested, calling
-	 * spinlock_exit() will simply adjust the counts without allowing
-	 * spin lock using code to interrupt us.
-	 */
-	spinlock_exit();
-	KASSERT(curthread->td_md.md_spinlock_count == 1, ("invalid count"));
-
-	PCPU_SET(switchtime, cpu_ticks());
-	PCPU_SET(switchticks, ticks);
-
-	cpu_throw(NULL, choosethread());	/* doesn't return */
+	/* enter the scheduler */
+	sched_throw(NULL);
 
 	panic("scheduler returned us to %s", __func__);
 	/* NOTREACHED */
@@ -1194,12 +1178,12 @@ ipi_bitmap_handler(struct trapframe frame)
 #ifdef COUNT_IPIS
 		(*ipi_preempt_counts[cpu])++;
 #endif
-		mtx_lock_spin(&sched_lock);
+		thread_lock(running_thread);
 		if (running_thread->td_critnest > 1) 
 			running_thread->td_owepreempt = 1;
 		else 		
 			mi_switch(SW_INVOL | SW_PREEMPT, NULL);
-		mtx_unlock_spin(&sched_lock);
+		thread_unlock(running_thread);
 	}
 
 	if (ipi_bitmap & (1 << IPI_AST)) {

sys/ia64/ia64/mp_machdep.c

@@ -110,16 +110,6 @@ ia64_ap_startup(void)
 	KASSERT(PCPU_GET(idlethread) != NULL, ("no idle thread"));
 	PCPU_SET(curthread, PCPU_GET(idlethread));
 
-	/*
-	 * Correct spinlock nesting.  The idle thread context that we are
-	 * borrowing was created so that it would start out with a single
-	 * spin lock (sched_lock) held in fork_trampoline().  Since we
-	 * don't have any locks and explicitly acquire locks when we need
-	 * to, the nesting count will be off by 1.
-	 */
-	curthread->td_md.md_spinlock_count = 0;
-	critical_exit();
-
 	/*
 	 * Get and save the CPU specific MCA records. Should we get the
 	 * MCA state for each processor, or just the CMC state?
@@ -133,17 +123,12 @@ ia64_ap_startup(void)
 
 	CTR1(KTR_SMP, "SMP: cpu%d launched", PCPU_GET(cpuid));
 
-	mtx_lock_spin(&sched_lock);
-
-	PCPU_SET(switchtime, cpu_ticks());
-	PCPU_SET(switchticks, ticks);
-
 	ia64_set_tpr(0);
 
 	/* kick off the clock on this AP */
 	pcpu_initclock();
 
-	cpu_throw(NULL, choosethread());
+	sched_throw(NULL);
 	/* NOTREACHED */
 }
 

sys/sparc64/sparc64/mp_machdep.c

@@ -364,12 +364,8 @@ cpu_mp_bootstrap(struct pcpu *pc)
 	while (csa->csa_count != 0)
 		;
 
-	/* ok, now grab sched_lock and enter the scheduler */
-	mtx_lock_spin(&sched_lock);
-	spinlock_exit();
-	PCPU_SET(switchtime, cpu_ticks());
-	PCPU_SET(switchticks, ticks);
-	cpu_throw(NULL, choosethread());	/* doesn't return */
+	/* ok, now enter the scheduler */
+	sched_throw(NULL);
 }
 
 void

sys/sun4v/sun4v/mp_machdep.c

@@ -403,13 +403,8 @@ cpu_mp_bootstrap(struct pcpu *pc)
 
 	while (csa->csa_count != 0)
 		;
-	/* ok, now grab sched_lock and enter the scheduler */
-	mtx_lock_spin(&sched_lock);
-	spinlock_exit();
-	PCPU_SET(switchtime, cpu_ticks());
-	PCPU_SET(switchticks, ticks);
-
-	cpu_throw(NULL, choosethread());	/* doesn't return */
+	/* ok, now enter the scheduler */
+	sched_throw(NULL);
 }
 
 void
@@ -460,13 +455,12 @@ cpu_ipi_preempt(struct trapframe *tf)
 {
 	struct thread *running_thread = curthread;
 
-	mtx_lock_spin(&sched_lock);
+	thread_lock(running_thread);
 	if (running_thread->td_critnest > 1)
 		running_thread->td_owepreempt = 1;
 	else
 		mi_switch(SW_INVOL | SW_PREEMPT, NULL);
-	mtx_unlock_spin(&sched_lock);
-
+	thread_unlock(running_thread);
 }
 
 void