void
forward_signal(struct thread *td)
{
int id;
/*
* signotify() has already set TDF_ASTPENDING and TDF_NEEDSIGCHECK on
* this thread, so all we need to do is poke it if it is currently
* executing so that it executes ast().
*/
THREAD_LOCK_ASSERT(td, MA_OWNED);
KASSERT(TD_IS_RUNNING(td),
("forward_signal: thread is not TDS_RUNNING"));
CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);
if (!smp_started || cold || panicstr)
return;
if (!forward_signal_enabled)
return;
/* No need to IPI ourself. */
if (td == curthread)
return;
id = td->td_oncpu;
if (id == NOCPU)
return;
ipi_cpu(id, IPI_AST);
}
/*
* Arrange to reschedule if necessary, taking the priorities and
* schedulers into account.
*/
static void
maybe_resched(struct thread *td)
{
THREAD_LOCK_ASSERT(td, MA_OWNED);
if (td->td_priority < curthread->td_priority)
curthread->td_flags |= TDF_NEEDRESCHED;
}
struct mtx *
thread_lock_block(struct thread *td)
{
struct mtx *lock;
THREAD_LOCK_ASSERT(td, MA_OWNED);
lock = td->td_lock;
td->td_lock = &blocked_lock;
mtx_unlock_spin(lock);
return (lock);
}
/*
* This function is called when a thread is about to be put on run queue
* because it has been made runnable or its priority has been adjusted. It
* determines if the new thread should be immediately preempted to. If so,
* it switches to it and eventually returns true. If not, it returns false
* so that the caller may place the thread on an appropriate run queue.
*/
int
maybe_preempt(struct thread *td)
{
#ifdef PREEMPTION
struct thread *ctd;
int cpri, pri;
/*
* The new thread should not preempt the current thread if any of the
* following conditions are true:
*
* - The kernel is in the throes of crashing (panicstr).
* - The current thread has a higher (numerically lower) or
* equivalent priority. Note that this prevents curthread from
* trying to preempt to itself.
* - It is too early in the boot for context switches (cold is set).
* - The current thread has an inhibitor set or is in the process of
* exiting. In this case, the current thread is about to switch
* out anyways, so there's no point in preempting. If we did,
* the current thread would not be properly resumed as well, so
* just avoid that whole landmine.
* - If the new thread's priority is not a realtime priority and
* the current thread's priority is not an idle priority and
* FULL_PREEMPTION is disabled.
*
* If all of these conditions are false, but the current thread is in
* a nested critical section, then we have to defer the preemption
* until we exit the critical section. Otherwise, switch immediately
* to the new thread.
*/
ctd = curthread;
THREAD_LOCK_ASSERT(td, MA_OWNED);
KASSERT((td->td_inhibitors == 0),
("maybe_preempt: trying to run inhibited thread"));
pri = td->td_priority;
cpri = ctd->td_priority;
if (panicstr != NULL || pri >= cpri || cold /* || dumping */ ||
TD_IS_INHIBITED(ctd))
return (0);
#ifndef FULL_PREEMPTION
if (pri > PRI_MAX_ITHD && cpri < PRI_MIN_IDLE)
return (0);
#endif
if (ctd->td_critnest > 1) {
CTR1(KTR_PROC, "maybe_preempt: in critical section %d",
ctd->td_critnest);
ctd->td_owepreempt = 1;
return (0);
}
/*
* Thread is runnable but not yet put on system run queue.
*/
MPASS(ctd->td_lock == td->td_lock);
MPASS(TD_ON_RUNQ(td));
TD_SET_RUNNING(td);
CTR3(KTR_PROC, "preempting to thread %p (pid %d, %s)\n", td,
td->td_proc->p_pid, td->td_name);
mi_switch(SW_INVOL | SW_PREEMPT | SWT_PREEMPT, td);
/*
* td's lock pointer may have changed. We have to return with it
* locked.
*/
spinlock_enter();
thread_unlock(ctd);
thread_lock(td);
spinlock_exit();
return (1);
#else
return (0);
#endif
}
/*
* Process an asynchronous software trap.
* This is relatively easy.
* This function will return with preemption disabled.
*/
void
ast(struct trapframe *framep)
{
struct thread *td;
struct proc *p;
int flags;
int sig;
td = curthread;
p = td->td_proc;
CTR3(KTR_SYSC, "ast: thread %p (pid %d, %s)", td, p->p_pid,
p->p_comm);
KASSERT(TRAPF_USERMODE(framep), ("ast in kernel mode"));
WITNESS_WARN(WARN_PANIC, NULL, "Returning to user mode");
mtx_assert(&Giant, MA_NOTOWNED);
THREAD_LOCK_ASSERT(td, MA_NOTOWNED);
td->td_frame = framep;
td->td_pticks = 0;
/*
* This updates the td_flag's for the checks below in one
* "atomic" operation with turning off the astpending flag.
* If another AST is triggered while we are handling the
* AST's saved in flags, the astpending flag will be set and
* ast() will be called again.
*/
thread_lock(td);
flags = td->td_flags;
td->td_flags &= ~(TDF_ASTPENDING | TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK |
TDF_NEEDRESCHED | TDF_ALRMPEND | TDF_PROFPEND | TDF_MACPEND);
thread_unlock(td);
PCPU_INC(cnt.v_trap);
if (td->td_ucred != p->p_ucred)
cred_update_thread(td);
if (td->td_pflags & TDP_OWEUPC && p->p_flag & P_PROFIL) {
addupc_task(td, td->td_profil_addr, td->td_profil_ticks);
td->td_profil_ticks = 0;
td->td_pflags &= ~TDP_OWEUPC;
}
#ifdef HWPMC_HOOKS
/* Handle Software PMC callchain capture. */
if (PMC_IS_PENDING_CALLCHAIN(td))
PMC_CALL_HOOK_UNLOCKED(td, PMC_FN_USER_CALLCHAIN_SOFT, (void *) framep);
#endif
if (flags & TDF_ALRMPEND) {
PROC_LOCK(p);
kern_psignal(p, SIGVTALRM);
PROC_UNLOCK(p);
}
if (flags & TDF_PROFPEND) {
PROC_LOCK(p);
kern_psignal(p, SIGPROF);
PROC_UNLOCK(p);
}
#ifdef MAC
if (flags & TDF_MACPEND)
mac_thread_userret(td);
#endif
if (flags & TDF_NEEDRESCHED) {
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(1, 1, __func__);
#endif
thread_lock(td);
sched_prio(td, td->td_user_pri);
mi_switch(SW_INVOL | SWT_NEEDRESCHED, NULL);
thread_unlock(td);
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(0, 1, __func__);
#endif
}
/*
* Check for signals. Unlocked reads of p_pendingcnt or
* p_siglist might cause process-directed signal to be handled
* later.
*/
if (flags & TDF_NEEDSIGCHK || p->p_pendingcnt > 0 ||
!SIGISEMPTY(p->p_siglist)) {
PROC_LOCK(p);
mtx_lock(&p->p_sigacts->ps_mtx);
while ((sig = cursig(td)) != 0)
postsig(sig);
mtx_unlock(&p->p_sigacts->ps_mtx);
PROC_UNLOCK(p);
}
/*
* We need to check to see if we have to exit or wait due to a
* single threading requirement or some other STOP condition.
*/
if (flags & TDF_NEEDSUSPCHK) {
PROC_LOCK(p);
thread_suspend_check(0);
PROC_UNLOCK(p);
}
if (td->td_pflags & TDP_OLDMASK) {
td->td_pflags &= ~TDP_OLDMASK;
kern_sigprocmask(td, SIG_SETMASK, &td->td_oldsigmask, NULL, 0);
}
userret(td, framep);
}
