From: mpi <mpi@openbsd.org>
Date: Mon, 18 Dec 2017 10:10:53 +0000 (+0000)
Subject: Revert support for multiple threads to enter kqueue_scan() in parallel.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=106b92f9d975072f44026d4d77dfbdcedc8f62c5;p=openbsd

Revert support for multiple threads to enter kqueue_scan() in parallel.

It is not clear if this change is responsible for the lockups experienced
by dhill@ and jcs@ but since we're no longer grabbing the socket lock in
kqueue(2) filters there's no need for this change.
---

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index b13feef56a4..96663208e71 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_event.c,v 1.82 2017/11/04 14:13:53 mpi Exp $	*/
+/*	$OpenBSD: kern_event.c,v 1.83 2017/12/18 10:10:53 mpi Exp $	*/
 
 /*-
  * Copyright (c) 1999,2000,2001 Jonathan Lemon <jlemon@FreeBSD.org>
@@ -84,8 +84,6 @@ void	knote_attach(struct knote *kn, struct filedesc *fdp);
 void	knote_drop(struct knote *kn, struct proc *p, struct filedesc *fdp);
 void	knote_enqueue(struct knote *kn);
 void	knote_dequeue(struct knote *kn);
-int	knote_acquire(struct knote *kn);
-int	knote_release(struct knote *kn);
 #define knote_alloc() ((struct knote *)pool_get(&knote_pool, PR_WAITOK))
 #define knote_free(kn) pool_put(&knote_pool, (kn))
 
@@ -761,43 +759,27 @@ start:
 		goto done;
 	}
 
-	marker.kn_filter = EVFILT_MARKER;
-	marker.kn_status = KN_PROCESSING;
 	TAILQ_INSERT_TAIL(&kq->kq_head, &marker, kn_tqe);
 	while (count) {
 		kn = TAILQ_FIRST(&kq->kq_head);
 		if (kn == &marker) {
-			TAILQ_REMOVE(&kq->kq_head, &marker, kn_tqe);
+			TAILQ_REMOVE(&kq->kq_head, kn, kn_tqe);
 			splx(s);
 			if (count == maxevents)
 				goto retry;
 			goto done;
 		}
-		if (kn->kn_filter == EVFILT_MARKER) {
-			struct knote *other_marker = kn;
-
-			/* Move some other threads marker past this kn */
-			kn = TAILQ_NEXT(other_marker, kn_tqe);
-			TAILQ_REMOVE(&kq->kq_head, kn, kn_tqe);
-			TAILQ_INSERT_BEFORE(other_marker, kn, kn_tqe);
-			continue;
-		}
-
-		if (!knote_acquire(kn))
-			continue;
 
 		TAILQ_REMOVE(&kq->kq_head, kn, kn_tqe);
 		kq->kq_count--;
 
 		if (kn->kn_status & KN_DISABLED) {
 			kn->kn_status &= ~KN_QUEUED;
-			knote_release(kn);
 			continue;
 		}
 		if ((kn->kn_flags & EV_ONESHOT) == 0 &&
 		    kn->kn_fop->f_event(kn, 0) == 0) {
 			kn->kn_status &= ~(KN_QUEUED | KN_ACTIVE);
-			knote_release(kn);
 			continue;
 		}
 		*kevp = kn->kn_kevent;
@@ -817,11 +799,9 @@ start:
 			if (kn->kn_flags & EV_DISPATCH)
 				kn->kn_status |= KN_DISABLED;
 			kn->kn_status &= ~(KN_QUEUED | KN_ACTIVE);
-			knote_release(kn);
 		} else {
 			TAILQ_INSERT_TAIL(&kq->kq_head, kn, kn_tqe);
 			kq->kq_count++;
-			knote_release(kn);
 		}
 		count--;
 		if (nkev == KQ_NEVENTS) {
@@ -975,41 +955,6 @@ kqueue_wakeup(struct kqueue *kq)
 		KNOTE(&kq->kq_sel.si_note, 0);
 }
 
-/*
- * Acquire a knote, return non-zero on success, 0 on failure.
- *
- * If we cannot acquire the knote we sleep and return 0.  The knote
- * may be stale on return in this case and the caller must restart
- * whatever loop they are in.
- */
-int
-knote_acquire(struct knote *kn)
-{
-	if (kn->kn_status & KN_PROCESSING) {
-		kn->kn_status |= KN_WAITING;
-		tsleep(kn, 0, "kqepts", hz);
-		/* knote may be stale now */
-		return (0);
-	}
-	kn->kn_status |= KN_PROCESSING;
-	return (1);
-}
-
-/*
- * Release an acquired knote, clearing KN_PROCESSING.
- */
-int
-knote_release(struct knote *kn)
-{
-	if (kn->kn_status & KN_WAITING) {
-		kn->kn_status &= ~KN_WAITING;
-		wakeup(kn);
-	}
-	kn->kn_status &= ~KN_PROCESSING;
-	/* kn should not be accessed anymore */
-	return (0);
-}
-
 /*
  * activate one knote.
  */
@@ -1041,8 +986,6 @@ knote_remove(struct proc *p, struct klist *list)
 	struct knote *kn;
 
 	while ((kn = SLIST_FIRST(list)) != NULL) {
-		if (!knote_acquire(kn))
-			continue;
 		kn->kn_fop->f_detach(kn);
 		knote_drop(kn, p, p->p_fd);
 	}
diff --git a/sys/sys/event.h b/sys/sys/event.h
index 0bcf648b60c..a3036a8aa13 100644
--- a/sys/sys/event.h
+++ b/sys/sys/event.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: event.h,v 1.27 2017/11/04 14:13:53 mpi Exp $	*/
+/*	$OpenBSD: event.h,v 1.28 2017/12/18 10:10:53 mpi Exp $	*/
 
 /*-
  * Copyright (c) 1999,2000,2001 Jonathan Lemon <jlemon@FreeBSD.org>
@@ -121,8 +121,6 @@ SLIST_HEAD(klist, knote);
 
 #ifdef _KERNEL
 
-#define EVFILT_MARKER	0xF			/* placemarker for tailq */
-
 /*
  * hint flag for in-kernel use - must not equal any existing note
  */
@@ -168,8 +166,6 @@ struct knote {
 #define KN_QUEUED	0x0002			/* event is on queue */
 #define KN_DISABLED	0x0004			/* event is disabled */
 #define KN_DETACHED	0x0008			/* knote is detached */
-#define KN_PROCESSING	0x0010			/* event processing in prog */
-#define KN_WAITING	0x0020			/* waiting on processing */
 
 #define kn_id		kn_kevent.ident
 #define kn_filter	kn_kevent.filter