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Date:      Fri, 26 Jun 2009 17:36:43 +0400
From:      Stanislav Sedov <stas@FreeBSD.org>
To:        Thomas Backman <serenity@exscape.org>
Cc:        freebsd-current@freebsd.org, Artem Belevich <fbsdlist@src.cx>
Subject:   Re: ZFS : panic("sleeping thread")
Message-ID:  <20090626173643.b4950bc8.stas@FreeBSD.org>
In-Reply-To: <AEA6B136-7464-4A8A-A683-69D651B4625B@exscape.org>
References:  <ed91d4a80905271058mbc1fc68g184def5097080cbc@mail.gmail.com> <993B7B5B-1B6B-48A5-8425-6A1D071335A9@exscape.org> <20090626164639.71a34f62.stas@FreeBSD.org> <AEA6B136-7464-4A8A-A683-69D651B4625B@exscape.org>

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On Fri, 26 Jun 2009 14:59:18 +0200
Thomas Backman <serenity@exscape.org> mentioned:

> I could (and might, too), but unfortunately (well, I guess...) I  
> haven't been able to reproduce this, despite writing a script to  
> really stress test it. It's either pretty darn random, or I was simply  
> wrong about the rollback being involved. I've only gotten it once  
> since I started using -CURRENT in early May(?) so I don't think I  
> could tell whether the patch helps or not. :(
> 

I think this could be triggered by tailing the file on ZFS that is being
writed with reasonable disk activity.

BTW, file I sent previously was incorrect.  I attached the rigth one.

Thanks!
-- 
Stanislav Sedov
ST4096-RIPE

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diff -r b446ba89e2b9 src/sys/kern/kern_event.c
--- a/src/sys/kern/kern_event.c	Tue Jun 23 17:00:09 2009 +0400
+++ b/src/sys/kern/kern_event.c	Fri Jun 26 17:32:43 2009 +0400
@@ -1608,17 +1608,18 @@
  * first.
  */
 void
-knote(struct knlist *list, long hint, int islocked)
+knote(struct knlist *list, long hint, int lockflags)
 {
 	struct kqueue *kq;
 	struct knote *kn;
+	int error;
 
 	if (list == NULL)
 		return;
 
-	KNL_ASSERT_LOCK(list, islocked);
+	KNL_ASSERT_LOCK(list, lockflags & KNF_LISTLOCKED);
 
-	if (!islocked) 
+	if ((lockflags & KNF_LISTLOCKED) == 0)
 		list->kl_lock(list->kl_lockarg); 
 
 	/*
@@ -1633,17 +1634,28 @@
 		kq = kn->kn_kq;
 		if ((kn->kn_status & KN_INFLUX) != KN_INFLUX) {
 			KQ_LOCK(kq);
-			if ((kn->kn_status & KN_INFLUX) != KN_INFLUX) {
+			if ((kn->kn_status & KN_INFLUX) == KN_INFLUX) {
+				KQ_UNLOCK(kq);
+			} else if ((lockflags & KNF_NOKQLOCK) != 0) {
+				kn->kn_status |= KN_INFLUX;
+				KQ_UNLOCK(kq);
+				error = kn->kn_fop->f_event(kn, hint);
+				KQ_LOCK(kq);
+				kn->kn_status &= ~KN_INFLUX;
+				if (error)
+					KNOTE_ACTIVATE(kn, 1);
+				KQ_UNLOCK_FLUX(kq);
+			} else {
 				kn->kn_status |= KN_HASKQLOCK;
 				if (kn->kn_fop->f_event(kn, hint))
 					KNOTE_ACTIVATE(kn, 1);
 				kn->kn_status &= ~KN_HASKQLOCK;
+				KQ_UNLOCK(kq);
 			}
-			KQ_UNLOCK(kq);
 		}
 		kq = NULL;
 	}
-	if (!islocked)
+	if ((lockflags & KNF_LISTLOCKED) == 0)
 		list->kl_unlock(list->kl_lockarg); 
 }
 
diff -r b446ba89e2b9 src/sys/sys/event.h
--- a/src/sys/sys/event.h	Tue Jun 23 17:00:09 2009 +0400
+++ b/src/sys/sys/event.h	Fri Jun 26 17:32:43 2009 +0400
@@ -135,8 +135,14 @@
 MALLOC_DECLARE(M_KQUEUE);
 #endif
 
-#define KNOTE(list, hist, lock)		knote(list, hist, lock)
-#define KNOTE_LOCKED(list, hint)	knote(list, hint, 1)
+/*
+ * Flags for knote call
+ */
+#define	KNF_LISTLOCKED	0x0001			/* knlist is locked */
+#define	KNF_NOKQLOCK	0x0002			/* do not keep KQ_LOCK */
+
+#define KNOTE(list, hist, flags)	knote(list, hist, flags)
+#define KNOTE_LOCKED(list, hint)	knote(list, hint, KNF_LISTLOCKED)
 #define KNOTE_UNLOCKED(list, hint)	knote(list, hint, 0)
 
 #define	KNLIST_EMPTY(list)		SLIST_EMPTY(&(list)->kl_list)
@@ -204,7 +210,7 @@
 struct proc;
 struct knlist;
 
-extern void	knote(struct knlist *list, long hint, int islocked);
+extern void	knote(struct knlist *list, long hint, int lockflags);
 extern void	knote_fork(struct knlist *list, int pid);
 extern void	knlist_add(struct knlist *knl, struct knote *kn, int islocked);
 extern void	knlist_remove(struct knlist *knl, struct knote *kn, int islocked);
diff -r b446ba89e2b9 src/sys/sys/mount.h
--- a/src/sys/sys/mount.h	Tue Jun 23 17:00:09 2009 +0400
+++ b/src/sys/sys/mount.h	Fri Jun 26 17:32:43 2009 +0400
@@ -633,7 +633,7 @@
 #define VFS_KNOTE_LOCKED(vp, hint) do					\
 {									\
 	if (((vp)->v_vflag & VV_NOKNOTE) == 0)				\
-		VN_KNOTE((vp), (hint), 1);				\
+		VN_KNOTE((vp), (hint), KNF_LISTLOCKED);			\
 } while (0)
 
 #define VFS_KNOTE_UNLOCKED(vp, hint) do					\
diff -r b446ba89e2b9 src/sys/sys/vnode.h
--- a/src/sys/sys/vnode.h	Tue Jun 23 17:00:09 2009 +0400
+++ b/src/sys/sys/vnode.h	Fri Jun 26 17:32:43 2009 +0400
@@ -222,9 +222,10 @@
 #define VN_KNOTE(vp, b, a)					\
 	do {							\
 		if (!VN_KNLIST_EMPTY(vp))			\
-			KNOTE(&vp->v_pollinfo->vpi_selinfo.si_note, (b), (a)); \
+			KNOTE(&vp->v_pollinfo->vpi_selinfo.si_note, (b), \
+			    (a) | KNF_NOKQLOCK);		\
 	} while (0)
-#define	VN_KNOTE_LOCKED(vp, b)		VN_KNOTE(vp, b, 1)
+#define	VN_KNOTE_LOCKED(vp, b)		VN_KNOTE(vp, b, KNF_LISTLOCKED)
 #define	VN_KNOTE_UNLOCKED(vp, b)	VN_KNOTE(vp, b, 0)
 
 /*

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