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

[Antti Kantee]

Module Name:    src
Committed By:   pooka
Date:           Fri Sep  4 16:41:39 UTC 2009

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

Log Message:
Actually, we cannot release the megalock before we take sleepermtx,
since that opens a race window for non-mpsafe code, so do it after.
Additionally, we cannot call mutex_enter() for sleepermtx, since
ltsleep/mtsleep should not block (i.e. release kernel lock) before
actually blocking, so busyloop in mutex_tryenter().  Finally, when
waking up, take kernel lock back only *after* releasing sleepermtx
to avoid deadlock against another thread holding the kernel lock
and wanting sleepermtx.


To generate a diff of this commit:
cvs rdiff -u -r1.15 -r1.16 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:1.15 src/sys/rump/librump/rumpkern/ltsleep.c:1.16
--- src/sys/rump/librump/rumpkern/ltsleep.c:1.15	Fri Sep  4 13:58:57 2009
+++ src/sys/rump/librump/rumpkern/ltsleep.c	Fri Sep  4 16:41:39 2009
@@ -1,4 +1,4 @@
-/*	$NetBSD: ltsleep.c,v 1.15 2009/09/04 13:58:57 pooka Exp $	*/
+/*	$NetBSD: ltsleep.c,v 1.16 2009/09/04 16:41:39 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 1.15 2009/09/04 13:58:57 pooka Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ltsleep.c,v 1.16 2009/09/04 16:41:39 pooka Exp $");
 
 #include <sys/param.h>
 #include <sys/proc.h>
@@ -58,12 +58,12 @@
 	struct ltsleeper lts;
 	int nlocks;
 
-	KERNEL_UNLOCK_ALL(curlwp, &nlocks);
-
 	lts.id = ident;
 	cv_init(&lts.cv, NULL);
 
-	mutex_enter(&sleepermtx);
+	while (!mutex_tryenter(&sleepermtx))
+		continue;
+	KERNEL_UNLOCK_ALL(curlwp, &nlocks);
 	if (slock)
 		simple_unlock(slock);
 	LIST_INSERT_HEAD(&sleepers, &lts, entries);
@@ -76,10 +76,11 @@
 
 	cv_destroy(&lts.cv);
 
+	KERNEL_LOCK(nlocks, curlwp);
+
 	if (slock && (prio & PNORELOCK) == 0)
 		simple_lock(slock);
 
-	KERNEL_LOCK(nlocks, curlwp);
 	return 0;
 }
 
@@ -90,12 +91,12 @@
 	struct ltsleeper lts;
 	int nlocks;
 
-	KERNEL_UNLOCK_ALL(curlwp, &nlocks);
-
 	lts.id = ident;
 	cv_init(&lts.cv, NULL);
 
-	mutex_enter(&sleepermtx);
+	while (!mutex_tryenter(&sleepermtx))
+		continue;
+	KERNEL_UNLOCK_ALL(curlwp, &nlocks);
 	LIST_INSERT_HEAD(&sleepers, &lts, entries);
 
 	/* protected by sleepermtx */
@@ -107,10 +108,11 @@
 
 	cv_destroy(&lts.cv);
 
+	KERNEL_LOCK(nlocks, curlwp);
+
 	if ((prio & PNORELOCK) == 0)
 		mutex_enter(lock);
 
-	KERNEL_LOCK(nlocks, curlwp);
 	return 0;
 }