Add a new sched_clear_name() method to the scheduler interface to clear

the cached name used for KTR_SCHED traces when a thread's name changes.
This way KTR_SCHED traces (and thus schedgraph) will notice when a thread's
name changes, most commonly via execve().

MFC after:	2 weeks

sys/kern/kern_exec.c

@@ -57,6 +57,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/pioctl.h>
 #include <sys/namei.h>
 #include <sys/resourcevar.h>
+#include <sys/sched.h>
 #include <sys/sdt.h>
 #include <sys/sf_buf.h>
 #include <sys/syscallsubr.h>
@@ -636,6 +637,9 @@ do_execve(td, args, mac_p)
 	else if (vn_commname(binvp, p->p_comm, sizeof(p->p_comm)) != 0)
 		bcopy(fexecv_proc_title, p->p_comm, sizeof(fexecv_proc_title));
 	bcopy(p->p_comm, td->td_name, sizeof(td->td_name));
+#ifdef KTR
+	sched_clear_tdname(td);
+#endif
 
 	/*
 	 * mark as execed, wakeup the process that vforked (if any) and tell

sys/kern/kern_intr.c

@@ -180,6 +180,9 @@ ithread_update(struct intr_thread *ithd)
 
 	/* Update name and priority. */
 	strlcpy(td->td_name, ie->ie_fullname, sizeof(td->td_name));
+#ifdef KTR
+	sched_clear_tdname(td);
+#endif
 	thread_lock(td);
 	sched_prio(td, pri);
 	thread_unlock(td);

sys/kern/kern_kthread.c

@@ -115,6 +115,9 @@ kproc_create(void (*func)(void *), void *arg,
 	va_start(ap, fmt);
 	vsnprintf(td->td_name, sizeof(td->td_name), fmt, ap);
 	va_end(ap);
+#ifdef KTR
+	sched_clear_tdname(td);
+#endif
 
 	/* call the processes' main()... */
 	cpu_set_fork_handler(td, func, arg);
@@ -453,6 +456,9 @@ kproc_kthread_add(void (*func)(void *), void *arg,
 		va_start(ap, fmt);
 		vsnprintf(td->td_name, sizeof(td->td_name), fmt, ap);
 		va_end(ap);
+#ifdef KTR
+		sched_clear_tdname(td);
+#endif
 		return (0); 
 	}
 	va_start(ap, fmt);

sys/kern/kern_thr.c

@@ -548,6 +548,9 @@ sys_thr_set_name(struct thread *td, struct thr_set_name_args *uap)
 	if (ttd == NULL)
 		return (ESRCH);
 	strcpy(ttd->td_name, name);
+#ifdef KTR
+	sched_clear_tdname(ttd);
+#endif
 	PROC_UNLOCK(p);
 	return (error);
 }

sys/kern/sched_4bsd.c

@@ -1614,6 +1614,17 @@ sched_tdname(struct thread *td)
 #endif
 }
 
+#ifdef KTR
+void
+sched_clear_tdname(struct thread *td)
+{
+	struct td_sched *ts;
+
+	ts = td->td_sched;
+	ts->ts_name[0] = '\0';
+}
+#endif
+
 void
 sched_affinity(struct thread *td)
 {

sys/kern/sched_ule.c

@@ -2684,6 +2684,17 @@ sched_tdname(struct thread *td)
 #endif
 }
 
+#ifdef KTR
+void
+sched_clear_tdname(struct thread *td)
+{
+	struct td_sched *ts;
+
+	ts = td->td_sched;
+	ts->ts_name[0] = '\0';
+}
+#endif
+
 #ifdef SMP
 
 /*

sys/sys/sched.h

@@ -138,6 +138,9 @@ int	sched_sizeof_thread(void);
  * functions.
  */
 char	*sched_tdname(struct thread *td);
+#ifdef KTR
+void	sched_clear_tdname(struct thread *td);
+#endif
 
 static __inline void
 sched_pin(void)