CVS commit: src/sys/rump/librump/rumpkern

[Antti Kantee]

Module Name:    src
Committed By:   pooka
Date:           Sun Oct  4 17:40:34 UTC 2009

Modified Files:
        src/sys/rump/librump/rumpkern: ltsleep.c

Log Message:
Fix hopefully the last deadlock in the wretched piece of code:
since ltsleep abuses "while (!mutex_tryenter()) continue;" for NOT
releasing the kernel biglock before sleeping, we cannot do a normal
mutex_enter() in the wakeup path, or otherwise we might be a
situation where the sleeper holds the kernel lock and wants the
sleepermutex (and will not back down) and the wakeupper holds the
sleepermutex and wants the kernel lock.  So introduce kernel lock
backdown to the wakeup path.


To generate a diff of this commit:
cvs rdiff -u -r1.17 -r1.18 src/sys/rump/librump/rumpkern/ltsleep.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.


Modified files:

Index: src/sys/rump/librump/rumpkern/ltsleep.c
diff -u src/sys/rump/librump/rumpkern/ltsleep.c:1.17 src/sys/rump/librump/rumpkern/ltsleep.c:1.18
--- src/sys/rump/librump/rumpkern/ltsleep.c:1.17	Fri Sep  4 16:42:19 2009
+++ src/sys/rump/librump/rumpkern/ltsleep.c	Sun Oct  4 17:40:34 2009
@@ -1,4 +1,4 @@
-/*	$NetBSD: ltsleep.c,v 1.17 2009/09/04 16:42:19 pooka Exp $	*/
+/*	$NetBSD: ltsleep.c,v 1.18 2009/10/04 17:40:34 pooka Exp $	*/
 
 /*
  * Copyright (c) 2007 Antti Kantee.  All Rights Reserved.
@@ -29,7 +29,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: ltsleep.c,v 1.17 2009/09/04 16:42:19 pooka Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ltsleep.c,v 1.18 2009/10/04 17:40:34 pooka Exp $");
 
 #include <sys/param.h>
 #include <sys/proc.h>
@@ -116,33 +116,37 @@
 	return 0;
 }
 
-void
-wakeup(wchan_t ident)
+static void
+do_wakeup(wchan_t ident, void (*wakeupfn)(kcondvar_t *))
 {
 	struct ltsleeper *ltsp;
+	int nlocks;
 
-	mutex_enter(&sleepermtx);
+	while (!mutex_tryenter(&sleepermtx)) {
+		KERNEL_UNLOCK_ALL(curlwp, &nlocks);
+		yield();
+		KERNEL_LOCK(nlocks, curlwp);
+	}
 	LIST_FOREACH(ltsp, &sleepers, entries) {
 		if (ltsp->id == ident) {
-			cv_broadcast(&ltsp->cv);
+			wakeupfn(&ltsp->cv);
 		}
 	}
 	mutex_exit(&sleepermtx);
 }
 
 void
+wakeup(wchan_t ident)
+{
+
+	do_wakeup(ident, cv_broadcast);
+}
+
+void
 wakeup_one(wchan_t ident)
 {
-	struct ltsleeper *ltsp;
 
-	mutex_enter(&sleepermtx);
-	LIST_FOREACH(ltsp, &sleepers, entries) {
-		if (ltsp->id == ident) {
-			cv_signal(&ltsp->cv);
-			break;
-		}
-	}
-	mutex_exit(&sleepermtx);
+	do_wakeup(ident, cv_signal);
 }
 
 void