Date: Tue, 20 Apr 1999 11:16:34 -0700 From: John Plevyak <jplevyak@inktomi.com> To: Luoqi Chen <luoqi@watermarkgroup.com>, hackers@FreeBSD.ORG, jplevyak@inktomi.com Subject: Re: flock + kernel threads bug Message-ID: <19990420111634.D10370@proxydev.inktomi.com> In-Reply-To: <199904201759.NAA15897@lor.watermarkgroup.com>; from Luoqi Chen on Tue, Apr 20, 1999 at 01:59:58PM -0400 References: <199904201759.NAA15897@lor.watermarkgroup.com>
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I sumbmitted a bug: kern/10265 it includes a description,
a program to repro and a patch.
The problem is:
releases of file locks depend on the close coming from the
same PID as took out the lock. Since kernel threads have
different PIDs it is possible for a peer thread to close
the file locked by another peer. This results in the file
lock not being cleared.
The patch does:
1. to use p->p_leader as the PID for file locking,
2. to use p->p_leader->p_flag & P_ADVLOCK to determine if locks are held
3. ensure that p->p_leader does not complete exit1() before
all the peers.
The full patch is in the bug report. I can send it to you
also if that is more convenient.
The patch in the bug report is non-optimal since it wakes up
the leader for each child instead of the just the last one.
If you change the last lines to:
if(p->p_leader->p_peers) {
q = p->p_leader;
while(q->p_peers != p)
q = q->p_peers;
q->p_peers = p->p_peers;
if (!p->p_leader->p_peers)
wakeup((caddr_t)p->p_leader);
}
from
+ if(p->p_leader->p_peers) {
+ q = p->p_leader;
+ while(q->p_peers != p)
+ q = q->p_peers;
+ q->p_peers = p->p_peers;
+ wakeup((caddr_t)p->p_leader);
+ }
This fixes it.
Thanx!
john
On Tue, Apr 20, 1999 at 01:59:58PM -0400, Luoqi Chen wrote:
> > Currently, kernel threads + flock does not work. The lock is not
> > necessarily released with the multi-threaded application shuts down.
> >
> Could you elaborate on the problem?
>
> > I have a patch which I have been running for a month now with no problems;
> > who might I send it to to get it reviewed/committed?
> >
> You could file a bug reports, see send-pr(1). Or you can send to me, I'm
> very interested in seeing it.
>
> > It would greatly simplify the installation of our multi-threaded apps
> > on FreeBSD if a kernel patch was not required. Not to mention a
> > general increase in confidence to have them work with FreeBSD "out-of-the-box".
> >
> > john
> >
> > --
> > John Bradley Plevyak, PhD, jplevyak@inktomi.com, PGP KeyID: 051130BD
> > Inktomi Corporation, 1900 S. Norfolk Street, Suite 310, San Mateo, CA 94403
> > W:(650)653-2830 F:(650)653-2889 P:(888)491-1332/5103192436.4911332@pagenet.net
> >
> -lq
>
>
> To Unsubscribe: send mail to majordomo@FreeBSD.org
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--
John Bradley Plevyak, PhD, jplevyak@inktomi.com, PGP KeyID: 051130BD
Inktomi Corporation, 1900 S. Norfolk Street, Suite 310, San Mateo, CA 94403
W:(650)653-2830 F:(650)653-2889 P:(888)491-1332/5103192436.4911332@pagenet.net
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