Date: Fri, 11 Aug 2006 18:20:41 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: Divacky Roman <xdivac02@stud.fit.vutbr.cz>, Perforce Change Reviews <perforce@freebsd.org>, Roman Divacky <rdivacky@freebsd.org> Subject: Re: PERFORCE change 103633 for review Message-ID: <20060811181817.C8215@fledge.watson.org> In-Reply-To: <200608111249.44686.jhb@freebsd.org> References: <200608111110.k7BBAxIO059339@repoman.freebsd.org> <20060811124027.K45647@fledge.watson.org> <20060811121314.GA85207@stud.fit.vutbr.cz> <200608111249.44686.jhb@freebsd.org>
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On Fri, 11 Aug 2006, John Baldwin wrote: >> I think the main problem (which is now fixed) was with this: >> >> copyin(addr, val1); >> if (val1 == val2) >> .... >> >> being non-atomic. On the other hand I tried to use other locks other then >> Giant and it didnt work. I hope to investigate that later. Now I have this >> working and my focus is elsewhere. > > No, what you have done is wrong. The idea of doing copyin() and then > compare is just plain not going to work. :) You will need to use casuptr() > or the like similar to the umtx code. This is assuming that a futex can be > manipulated from userland w/o entering the kernel. I assume that we can basically just do whatever Linux does here for synchronization... Robert N M Watson Computer Laboratory University of Cambridge
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