Introduce a mechanism to suspend/resume system processes. Suspend syncer

and bufdaemon prior to disk sync during system shutdown.

sys/kern/kern_kthread.c

@@ -30,6 +30,7 @@
 #include <sys/systm.h>
 #include <sys/proc.h>
 #include <sys/kthread.h>
+#include <sys/signalvar.h>
 #include <sys/unistd.h>
 #include <sys/wait.h>
 
@@ -97,3 +98,42 @@ kthread_exit(int ecode)
 	exit1(curproc, W_EXITCODE(ecode, 0));
 }
 
+/*
+ * Advise a kernel process to suspend (or resume) in its main loop.
+ * Participation is voluntary.
+ */
+int
+suspend_kproc(struct proc *p, int timo)
+{
+	/*
+	 * Make sure this is indeed a system process and we can safely
+	 * use the p_siglist field.
+	 */
+	if ((p->p_flag & P_SYSTEM) == 0)
+		return (EINVAL);
+	SIGADDSET(p->p_siglist, SIGSTOP);
+	return tsleep((caddr_t)&p->p_siglist, PPAUSE, "suspkp", timo);
+}
+
+int
+resume_kproc(struct proc *p)
+{
+	/*
+	 * Make sure this is indeed a system process and we can safely
+	 * use the p_siglist field.
+	 */
+	if ((p->p_flag & P_SYSTEM) == 0)
+		return (EINVAL);
+	SIGDELSET(p->p_siglist, SIGSTOP);
+	wakeup((caddr_t)&p->p_siglist);
+	return (0);
+}
+
+void
+kproc_suspend_loop(struct proc *p)
+{
+	while (SIGISMEMBER(p->p_siglist, SIGSTOP)) {
+		wakeup((caddr_t)&p->p_siglist);
+		tsleep((caddr_t)&p->p_siglist, PPAUSE, "kpsusp", 0);
+	}
+}

sys/kern/kern_shutdown.c

@@ -52,6 +52,7 @@
 #include <sys/proc.h>
 #include <sys/vnode.h>
 #include <sys/kernel.h>
+#include <sys/kthread.h>
 #include <sys/mount.h>
 #include <sys/queue.h>
 #include <sys/sysctl.h>
@@ -571,3 +572,34 @@ poweroff_wait(void *junk, int howto)
 		return;
 	DELAY(poweroff_delay * 1000);
 }
+
+/*
+ * Some system processes (e.g. syncer) need to be stopped at appropriate
+ * points in their main loops prior to a system shutdown, so that they
+ * won't interfere with the shutdown process (e.g. by holding a disk buf
+ * to cause sync to fail).  For each of these system processes, register
+ * shutdown_kproc() as a handler for one of shutdown events.
+ */
+static int kproc_shutdown_wait = 60;
+SYSCTL_INT(_kern_shutdown, OID_AUTO, kproc_shutdown_wait, CTLFLAG_RW,
+    &kproc_shutdown_wait, 0, "");
+
+void
+shutdown_kproc(void *arg, int howto)
+{
+	struct proc *p;
+	int error;
+
+	if (panicstr)
+		return;
+
+	p = (struct proc *)arg;
+	printf("Waiting (max %d seconds) for system process `%s' to stop...",
+	    kproc_shutdown_wait * hz, p->p_comm);
+	error = suspend_kproc(p, kproc_shutdown_wait);
+
+	if (error == EWOULDBLOCK)
+		printf("timed out\n");
+	else
+		printf("stopped\n");
+}

sys/kern/vfs_bio.c

@@ -29,13 +29,20 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
-#include <sys/kernel.h>
-#include <sys/sysctl.h>
-#include <sys/proc.h>
-#include <sys/kthread.h>
-#include <sys/vnode.h>
-#include <sys/vmmeter.h>
+#include <sys/buf.h>
+#include <sys/conf.h>
+#include <sys/eventhandler.h>
 #include <sys/lock.h>
+#include <sys/malloc.h>
+#include <sys/mount.h>
+#include <sys/kernel.h>
+#include <sys/kthread.h>
+#include <sys/proc.h>
+#include <sys/reboot.h>
+#include <sys/resourcevar.h>
+#include <sys/sysctl.h>
+#include <sys/vmmeter.h>
+#include <sys/vnode.h>
 #include <vm/vm.h>
 #include <vm/vm_param.h>
 #include <vm/vm_kern.h>
@@ -44,11 +51,6 @@
 #include <vm/vm_object.h>
 #include <vm/vm_extern.h>
 #include <vm/vm_map.h>
-#include <sys/buf.h>
-#include <sys/mount.h>
-#include <sys/malloc.h>
-#include <sys/resourcevar.h>
-#include <sys/conf.h>
 
 static MALLOC_DEFINE(M_BIOBUF, "BIO buffer", "BIO buffer");
 
@@ -1666,6 +1668,13 @@ static void
 buf_daemon()
 {
 	int s;
+
+	/*
+	 * This process needs to be suspended prior to shutdown sync.
+	 */
+	EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_kproc, bufdaemonproc,
+	    SHUTDOWN_PRI_LAST);
+
 	/*
 	 * This process is allowed to take the buffer cache to the limit
 	 */
@@ -1676,7 +1685,9 @@ buf_daemon()
 	bd_flushto = hidirtybuffers;	/* dynamically adjusted */
 	bd_flushinc = 1;
 
-	while (TRUE) {
+	for (;;) {
+		kproc_suspend_loop(bufdaemonproc);
+
 		bd_request = 0;
 
 		/*

sys/kern/vfs_export.c

@@ -46,20 +46,23 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/buf.h>
+#include <sys/conf.h>
+#include <sys/dirent.h>
+#include <sys/domain.h>
+#include <sys/eventhandler.h>
 #include <sys/fcntl.h>
 #include <sys/kernel.h>
-#include <sys/proc.h>
 #include <sys/kthread.h>
 #include <sys/malloc.h>
 #include <sys/mount.h>
+#include <sys/proc.h>
+#include <sys/reboot.h>
 #include <sys/socket.h>
-#include <sys/vnode.h>
 #include <sys/stat.h>
-#include <sys/buf.h>
-#include <sys/domain.h>
-#include <sys/dirent.h>
+#include <sys/sysctl.h>
 #include <sys/vmmeter.h>
-#include <sys/conf.h>
+#include <sys/vnode.h>
 
 #include <machine/limits.h>
 
@@ -72,7 +75,6 @@
 #include <vm/vm_pager.h>
 #include <vm/vnode_pager.h>
 #include <vm/vm_zone.h>
-#include <sys/sysctl.h>
 
 static MALLOC_DEFINE(M_NETADDR, "Export Host", "Export host address structure");
 
@@ -975,9 +977,14 @@ sched_sync(void)
 	int s;
 	struct proc *p = updateproc;
 
+	EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_kproc, p,
+	    SHUTDOWN_PRI_LAST);   
+
 	p->p_flag |= P_BUFEXHAUST;
 
 	for (;;) {
+		kproc_suspend_loop(p);
+
 		starttime = time_second;
 
 		/*

sys/kern/vfs_subr.c

@@ -46,20 +46,23 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/buf.h>
+#include <sys/conf.h>
+#include <sys/dirent.h>
+#include <sys/domain.h>
+#include <sys/eventhandler.h>
 #include <sys/fcntl.h>
 #include <sys/kernel.h>
-#include <sys/proc.h>
 #include <sys/kthread.h>
 #include <sys/malloc.h>
 #include <sys/mount.h>
+#include <sys/proc.h>
+#include <sys/reboot.h>
 #include <sys/socket.h>
-#include <sys/vnode.h>
 #include <sys/stat.h>
-#include <sys/buf.h>
-#include <sys/domain.h>
-#include <sys/dirent.h>
+#include <sys/sysctl.h>
 #include <sys/vmmeter.h>
-#include <sys/conf.h>
+#include <sys/vnode.h>
 
 #include <machine/limits.h>
 
@@ -72,7 +75,6 @@
 #include <vm/vm_pager.h>
 #include <vm/vnode_pager.h>
 #include <vm/vm_zone.h>
-#include <sys/sysctl.h>
 
 static MALLOC_DEFINE(M_NETADDR, "Export Host", "Export host address structure");
 
@@ -975,9 +977,14 @@ sched_sync(void)
 	int s;
 	struct proc *p = updateproc;
 
+	EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_kproc, p,
+	    SHUTDOWN_PRI_LAST);   
+
 	p->p_flag |= P_BUFEXHAUST;
 
 	for (;;) {
+		kproc_suspend_loop(p);
+
 		starttime = time_second;
 
 		/*

sys/sys/kthread.h

@@ -47,4 +47,9 @@ int     kthread_create __P((void (*)(void *), void *, struct proc **,
 	    const char *, ...)) __printflike(4, 5);
 void    kthread_exit __P((int)) __dead2;
 
+int	suspend_kproc __P((struct proc *, int));
+int	resume_kproc __P((struct proc *));
+void	kproc_suspend_loop __P((struct proc *));
+void	shutdown_kproc __P((void *, int));
+
 #endif