Function ast

freebsd/kern/subr_trap.c:201–364

* Process an asynchronous software trap. * This is relatively easy. * This function will return with preemption disabled. */

 * This function will return with preemption disabled.
 */
void
ast(struct trapframe *framep)
{
	struct thread *td;
	struct proc *p;
	int flags, sig;
	bool resched_sigs;

	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);
	VM_CNT_INC(v_trap);

	if (td->td_cowgen != p->p_cowgen)
		thread_cow_update(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)