sched: separate out schedinit_ap()
schedinit_ap() sets up an AP for a later call to sched_throw(NULL). Currently, ULE sets up some pcpu bits and fixes the idlethread lock with a call to sched_throw(NULL); this results in a window where curthread is setup in platforms' init_secondary(), but it has the wrong td_lock. Typical platform AP startup procedure looks something like: - Setup curthread - ... other stuff, including cpu_initclocks_ap() - Signal smp_started - sched_throw(NULL) to enter the scheduler cpu_initclocks_ap() may have callouts to process (e.g., nvme) and attempt to sched_add() for this AP, but this attempt fails because of the noted violated assumption leading to locking heartburn in sched_setpreempt(). Interrupts are still disabled until cpu_throw() so we're not really at risk of being preempted -- just let the scheduler in on it a little earlier as part of setting up curthread. Reviewed by: alfredo, kib, markj Triage help from: andrew, markj Smoke-tested by: alfredo (ppc), kevans (arm64, x86), mhorne (arm) Differential Revision: https://reviews.freebsd.org/D32797
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@ -182,6 +182,7 @@ init_secondary(int cpu)
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pc->pc_curthread = pc->pc_idlethread;
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pc->pc_curpcb = pc->pc_idlethread->td_pcb;
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set_curthread(pc->pc_idlethread);
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schedinit_ap();
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#ifdef VFP
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vfp_init();
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#endif
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@ -255,6 +255,7 @@ init_secondary(uint64_t cpu)
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/* Initialize curthread */
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KASSERT(PCPU_GET(idlethread) != NULL, ("no idle thread"));
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pcpup->pc_curthread = pcpup->pc_idlethread;
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schedinit_ap();
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/* Initialize curpmap to match TTBR0's current setting. */
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pmap0 = vmspace_pmap(&vmspace0);
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@ -678,6 +678,13 @@ schedinit(void)
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mtx_init(&sched_lock, "sched lock", NULL, MTX_SPIN);
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}
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void
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schedinit_ap(void)
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{
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/* Nothing needed. */
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}
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int
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sched_runnable(void)
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{
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@ -1743,6 +1743,26 @@ schedinit(void)
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ts0->ts_cpu = curcpu; /* set valid CPU number */
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}
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/*
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* schedinit_ap() is needed prior to calling sched_throw(NULL) to ensure that
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* the pcpu requirements are met for any calls in the period between curthread
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* initialization and sched_throw(). One can safely add threads to the queue
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* before sched_throw(), for instance, as long as the thread lock is setup
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* correctly.
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*
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* TDQ_SELF() relies on the below sched pcpu setting; it may be used only
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* after schedinit_ap().
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*/
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void
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schedinit_ap(void)
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{
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#ifdef SMP
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PCPU_SET(sched, DPCPU_PTR(tdq));
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#endif
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PCPU_GET(idlethread)->td_lock = TDQ_LOCKPTR(TDQ_SELF());
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}
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/*
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* This is only somewhat accurate since given many processes of the same
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* priority they will switch when their slices run out, which will be
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@ -2973,19 +2993,14 @@ sched_throw(struct thread *td)
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struct thread *newtd;
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struct tdq *tdq;
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tdq = TDQ_SELF();
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if (__predict_false(td == NULL)) {
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#ifdef SMP
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PCPU_SET(sched, DPCPU_PTR(tdq));
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#endif
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/* Correct spinlock nesting and acquire the correct lock. */
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tdq = TDQ_SELF();
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TDQ_LOCK(tdq);
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/* Correct spinlock nesting. */
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spinlock_exit();
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PCPU_SET(switchtime, cpu_ticks());
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PCPU_SET(switchticks, ticks);
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PCPU_GET(idlethread)->td_lock = TDQ_LOCKPTR(tdq);
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} else {
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tdq = TDQ_SELF();
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THREAD_LOCK_ASSERT(td, MA_OWNED);
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THREAD_LOCKPTR_ASSERT(td, TDQ_LOCKPTR(tdq));
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tdq_load_rem(tdq, td);
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@ -311,6 +311,7 @@ smp_init_secondary(u_int32_t cpuid)
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/* Initialize curthread. */
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KASSERT(PCPU_GET(idlethread) != NULL, ("no idle thread"));
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PCPU_SET(curthread, PCPU_GET(idlethread));
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schedinit_ap();
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mtx_lock_spin(&ap_boot_mtx);
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@ -35,6 +35,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/bus.h>
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#include <sys/pcpu.h>
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#include <sys/proc.h>
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#include <sys/sched.h>
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#include <sys/smp.h>
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#include <machine/bus.h>
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@ -134,6 +135,7 @@ cpudep_ap_bootstrap(void)
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#endif
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pcpup->pc_curpcb = pcpup->pc_curthread->td_pcb;
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sp = pcpup->pc_curpcb->pcb_sp;
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schedinit_ap();
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return (sp);
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}
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@ -35,6 +35,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/bus.h>
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#include <sys/pcpu.h>
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#include <sys/proc.h>
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#include <sys/sched.h>
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#include <sys/smp.h>
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#include <machine/pcb.h>
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@ -85,6 +86,7 @@ cpudep_ap_bootstrap()
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#endif
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pcpup->pc_curpcb = pcpup->pc_curthread->td_pcb;
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sp = pcpup->pc_curpcb->pcb_sp;
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schedinit_ap();
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/* XXX shouldn't the pcb_sp be checked/forced for alignment here?? */
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@ -248,6 +248,7 @@ init_secondary(uint64_t hart)
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/* Initialize curthread */
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KASSERT(PCPU_GET(idlethread) != NULL, ("no idle thread"));
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pcpup->pc_curthread = pcpup->pc_idlethread;
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schedinit_ap();
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/*
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* Identify current CPU. This is necessary to setup
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@ -226,6 +226,11 @@ SYSINIT(name, SI_SUB_LAST, SI_ORDER_MIDDLE, name ## _add_proc, NULL);
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* Fixup scheduler state for proc0 and thread0
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*/
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void schedinit(void);
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/*
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* Fixup scheduler state for secondary APs
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*/
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void schedinit_ap(void);
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#endif /* _KERNEL */
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/* POSIX 1003.1b Process Scheduling */
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@ -1040,6 +1040,7 @@ init_secondary_tail(void)
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/* Initialize curthread. */
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KASSERT(PCPU_GET(idlethread) != NULL, ("no idle thread"));
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PCPU_SET(curthread, PCPU_GET(idlethread));
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schedinit_ap();
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mtx_lock_spin(&ap_boot_mtx);
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