Date: Wed, 10 Nov 1999 00:30:12 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Assar Westerlund <assar@sics.se> Cc: current@FreeBSD.ORG Subject: Re: inconsistent and wrong locking in asleep() Message-ID: <Pine.BSF.4.10.9911092359380.10910-100000@alphplex.bde.org> In-Reply-To: <5l4sevrhxk.fsf@assaris.sics.se>
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> Why trying to debug some locking code of my own I enabled
> SIMPLELOCK_DEBUG, only to find out that I was getting lots of
> `simple_unlock: lock not held' in lockmgr -> acquire -> apause.
>
> Looking closer at `apause' it seems rather clear that it can cause
> this. I proposed simple change is below.
That's a really old bug. I fixed it a year or two ago in my version,
and optimised the !SMP case following a suggestion of tegge (waiting
for the lock is useless in the !SMP case).
Bruce
diff -c2 kern_lock.c~ kern_lock.c
*** kern_lock.c~ Tue Sep 28 06:06:16 1999
--- kern_lock.c Tue Sep 28 06:07:59 1999
***************
*** 104,125 ****
*/
static int
! apause(struct lock *lkp, int flags) {
! int lock_wait;
! lock_wait = LOCK_WAIT_TIME;
! for (; lock_wait > 0; lock_wait--) {
! int i;
! if ((lkp->lk_flags & flags) == 0)
! return 0;
simple_unlock(&lkp->lk_interlock);
! for (i = LOCK_SAMPLE_WAIT; i > 0; i--) {
! if ((lkp->lk_flags & flags) == 0) {
! simple_lock(&lkp->lk_interlock);
! if ((lkp->lk_flags & flags) == 0)
! return 0;
break;
! }
! }
}
! return 1;
}
--- 103,126 ----
*/
static int
! apause(struct lock *lkp, int flags)
! {
! #ifdef SMP
! int i, lock_wait;
! #endif
!
! if ((lkp->lk_flags & flags) == 0)
! return (0);
! #ifdef SMP
! for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
simple_unlock(&lkp->lk_interlock);
! for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
! if ((lkp->lk_flags & flags) == 0)
break;
! simple_lock(&lkp->lk_interlock);
! if ((lkp->lk_flags & flags) == 0)
! return (0);
}
! #endif
! return (1);
}
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