[src/trunk]: src/sys/rump/librump/rumpkern Actually, we cannot release the me...

[pooka <pooka%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/8d8ed61c664c
branches:  trunk
changeset: 747159:8d8ed61c664c
user:      pooka <pooka%NetBSD.org@localhost>
date:      Fri Sep 04 16:41:39 2009 +0000

description:
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.

diffstat:

 sys/rump/librump/rumpkern/ltsleep.c |  22 ++++++++++++----------
 1 files changed, 12 insertions(+), 10 deletions(-)

diffs (76 lines):

diff -r 330be95bbdd8 -r 8d8ed61c664c sys/rump/librump/rumpkern/ltsleep.c
--- a/sys/rump/librump/rumpkern/ltsleep.c       Fri Sep 04 16:21:24 2009 +0000
+++ b/sys/rump/librump/rumpkern/ltsleep.c       Fri Sep 04 16:41:39 2009 +0000
@@ -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;
 }