[src/trunk]: src/sys allow cv_signal() immediately followed by cv_destroy().

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

details:   https://anonhg.NetBSD.org/src/rev/14910966be0f
branches:  trunk
changeset: 354214:14910966be0f
user:      chs <chs%NetBSD.org@localhost>
date:      Thu Jun 08 01:09:52 2017 +0000

description:
allow cv_signal() immediately followed by cv_destroy().
this sequence is used by ZFS in a couple places and by supporting it
natively we can undo our local ZFS changes that avoided it.
note that this is only legal when all of the waiters use cv_wait()
and not any of the other variations, and lockdebug will catch
any violations of this rule.

diffstat:

 sys/kern/kern_condvar.c |  51 +++++++++++++++++++++++++++++++++++++++++-------
 sys/sys/lwp.h           |   3 +-
 2 files changed, 45 insertions(+), 9 deletions(-)

diffs (132 lines):

diff -r d6ac1a89e7f4 -r 14910966be0f sys/kern/kern_condvar.c
--- a/sys/kern/kern_condvar.c   Thu Jun 08 00:17:02 2017 +0000
+++ b/sys/kern/kern_condvar.c   Thu Jun 08 01:09:52 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_condvar.c,v 1.35 2015/08/07 06:22:12 uebayasi Exp $       */
+/*     $NetBSD: kern_condvar.c,v 1.36 2017/06/08 01:09:52 chs Exp $    */
 
 /*-
  * Copyright (c) 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -34,7 +34,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_condvar.c,v 1.35 2015/08/07 06:22:12 uebayasi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_condvar.c,v 1.36 2017/06/08 01:09:52 chs Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -65,9 +65,9 @@
 #define        CV_DEBUG_P(cv)  (CV_WMESG(cv) != nodebug)
 #define        CV_RA           ((uintptr_t)__builtin_return_address(0))
 
-static void    cv_unsleep(lwp_t *, bool);
-static void    cv_wakeup_one(kcondvar_t *);
-static void    cv_wakeup_all(kcondvar_t *);
+static void            cv_unsleep(lwp_t *, bool);
+static inline void     cv_wakeup_one(kcondvar_t *);
+static inline void     cv_wakeup_all(kcondvar_t *);
 
 static syncobj_t cv_syncobj = {
        SOBJ_SLEEPQ_SORTED,
@@ -86,6 +86,31 @@
 static const char deadcv[] = "deadcv";
 #ifdef LOCKDEBUG
 static const char nodebug[] = "nodebug";
+
+#define CV_LOCKDEBUG_HANDOFF(l, cv) cv_lockdebug_handoff(l, cv)
+#define CV_LOCKDEBUG_PROCESS(l, cv) cv_lockdebug_process(l, cv)
+
+static inline void
+cv_lockdebug_handoff(lwp_t *l, kcondvar_t *cv)
+{
+
+       if (CV_DEBUG_P(cv))
+               l->l_flag |= LW_CVLOCKDEBUG;
+}
+
+static inline void
+cv_lockdebug_process(lwp_t *l, kcondvar_t *cv)
+{
+
+       if ((l->l_flag & LW_CVLOCKDEBUG) == 0)
+               return;
+
+       l->l_flag &= ~LW_CVLOCKDEBUG;
+       LOCKDEBUG_UNLOCKED(true, cv, CV_RA, 0);
+}
+#else
+#define CV_LOCKDEBUG_HANDOFF(l, cv) __nothing
+#define CV_LOCKDEBUG_PROCESS(l, cv) __nothing
 #endif
 
 /*
@@ -214,8 +239,16 @@
        KASSERT(mutex_owned(mtx));
 
        cv_enter(cv, mtx, l);
+
+       /*
+        * We can't use cv_exit() here since the cv might be destroyed before
+        * this thread gets a chance to run.  Instead, hand off the lockdebug
+        * responsibility to the thread that wakes us up.
+        */
+
+       CV_LOCKDEBUG_HANDOFF(l, cv);
        (void)sleepq_block(0, false);
-       (void)cv_exit(cv, mtx, l, 0);
+       mutex_enter(mtx);
 }
 
 /*
@@ -302,7 +335,7 @@
                cv_wakeup_one(cv);
 }
 
-static void __noinline
+static inline void
 cv_wakeup_one(kcondvar_t *cv)
 {
        sleepq_t *sq;
@@ -321,6 +354,7 @@
        KASSERT(l->l_sleepq == sq);
        KASSERT(l->l_mutex == mp);
        KASSERT(l->l_wchan == cv);
+       CV_LOCKDEBUG_PROCESS(l, cv);
        sleepq_remove(sq, l);
        mutex_spin_exit(mp);
 
@@ -344,7 +378,7 @@
                cv_wakeup_all(cv);
 }
 
-static void __noinline
+static inline void
 cv_wakeup_all(kcondvar_t *cv)
 {
        sleepq_t *sq;
@@ -360,6 +394,7 @@
                KASSERT(l->l_mutex == mp);
                KASSERT(l->l_wchan == cv);
                next = TAILQ_NEXT(l, l_sleepchain);
+               CV_LOCKDEBUG_PROCESS(l, cv);
                sleepq_remove(sq, l);
        }
        mutex_spin_exit(mp);
diff -r d6ac1a89e7f4 -r 14910966be0f sys/sys/lwp.h
--- a/sys/sys/lwp.h     Thu Jun 08 00:17:02 2017 +0000
+++ b/sys/sys/lwp.h     Thu Jun 08 01:09:52 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: lwp.h,v 1.174 2017/04/21 15:10:35 christos Exp $       */
+/*     $NetBSD: lwp.h,v 1.175 2017/06/08 01:09:52 chs Exp $    */
 
 /*-
  * Copyright (c) 2001, 2006, 2007, 2008, 2009, 2010
@@ -231,6 +231,7 @@
 /* These flags are kept in l_flag. */
 #define        LW_IDLE         0x00000001 /* Idle lwp. */
 #define        LW_LWPCTL       0x00000002 /* Adjust lwpctl in userret */
+#define        LW_CVLOCKDEBUG  0x00000004 /* Waker does lockdebug */
 #define        LW_SINTR        0x00000080 /* Sleep is interruptible. */
 #define        LW_SYSTEM       0x00000200 /* Kernel thread */
 #define        LW_WSUSPEND     0x00020000 /* Suspend before return to user */