Date: Fri, 18 Apr 2003 02:28:32 -0400 (EDT) From: Daniel Eischen <eischen@pcnet1.pcnet.com> To: David Xu <davidxu@freebsd.org> Cc: freebsd-threads@freebsd.org Subject: Re: libpthread patch Message-ID: <Pine.GSO.4.10.10304180226040.5123-100000@pcnet1.pcnet.com> In-Reply-To: <005b01c30573$821cf6a0$f001a8c0@davidw2k>
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On Fri, 18 Apr 2003, David Xu wrote: > > ----- Original Message ----- > From: "Daniel Eischen" <eischen@pcnet1.pcnet.com> > To: "David Xu" <davidxu@freebsd.org> > Cc: <freebsd-threads@freebsd.org> > Sent: Friday, April 18, 2003 2:12 PM > Subject: Re: libpthread patch > > > > On Fri, 18 Apr 2003, David Xu wrote: > > > > > > > > ----- Original Message ----- > > > From: "Juli Mallett" <jmallett@FreeBSD.org> > > > To: "David Xu" <davidxu@freebsd.org> > > > Cc: "Daniel Eischen" <eischen@pcnet1.pcnet.com>; <freebsd-threads@freebsd.org> > > > Sent: Friday, April 18, 2003 2:04 PM > > > Subject: Re: libpthread patch > > > > > > > > > > * De: David Xu <davidxu@freebsd.org> [ Data: 2003-04-18 ] > > > > [ Subjecte: Re: libpthread patch ] > > > > > > There are a few issues we've got to go over, as well as > > > > > > looking closely at any locking order problems. > > > > > > > > > > > I have ever tried to port some kernel code to userland (e.g > > > > > mutex and witness), but now they were left there for > > > > > several days without be touched. > > > > > > > > This seems like overkill, in fact, it is by definition. If you > > > > want some primitive private-locks-only mutex tracing/auditing, > > > > I've done a bit of that and could give you some hints. Using the > > > > casuptr facility introduced by thr may be a good idea, no? It > > > > is known to work, and is relatively un-complex? Or am I missing > > > > something? > > > > > > I want to use code to detect LOR not just human eyes, I can accept > > > any reasonable method. > > > > We can do that now with the locks that I have in place. > > Each consumer of a lock has a "lock user". Threads and > > KSEs have an array of 3 lock users; probably 2 is enough > > because I don't think we need more than a nesting of 2. > > When you decrement the lock user index when releasing > > a lock, you make sure that the lock being released > > matches the one owned. In fact, I implemented it this > > way so you couldn't possible have lock order reversals. > > The locks will not work if you reverse them. > > > > witeness in kernel records locking order, not lock instance. > for example, at one time, code uses locking order > mutex1 mutex2, and release them, next time if another > code locks them in the order mutex2 mutex1, it would detect > it. Ahh, OK. There aren't that many locks used by the library. We can probably come up with something that does what you want. -- Dan Eischen
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