Date: Thu, 6 Aug 2009 17:33:22 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: jeff@FreeBSD.org, "Bjoern A. Zeeb" <bz@FreeBSD.org>, freebsd-current@FreeBSD.org, kib@FreeBSD.org, Navdeep Parhar <np@FreeBSD.org>, Navdeep Parhar <nparhar@gmail.com>, Larry Rosenman <ler@lerctr.org>, lstewart@FreeBSD.org Subject: Re: reproducible panic in netisr Message-ID: <alpine.BSF.2.00.0908061732360.62916@fledge.watson.org> In-Reply-To: <Pine.GSO.4.63.0908061038120.22077@muncher.cs.uoguelph.ca> References: <20090804225806.GA54680@hub.freebsd.org> <20090805054115.O93661@maildrop.int.zabbadoz.net> <20090805063417.GA10969@doormat.home> <alpine.BSF.2.00.0908060011490.59996@fledge.watson.org> <alpine.BSF.2.00.0908060834120.21318@thebighonker.lerctr.org> <alpine.BSF.2.00.0908061508520.62916@fledge.watson.org> <Pine.GSO.4.63.0908061038120.22077@muncher.cs.uoguelph.ca>
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On Thu, 6 Aug 2009, Rick Macklem wrote: > On Thu, 6 Aug 2009, Robert Watson wrote: > >> other places where we have very strong alignment requirements on >> i386/amd64, such as the td_ucred pointer that we check for change on system >> calls/traps to see if we need to refresh the thread's credential from the >> process credential. >> > Does this imply that the nfs/krpc hack of: > oldcred = td->td_ucred; > td->td_ucred = "some other cred ptr" > ... > td->td_ucred = oldcred; > > could be dangerous? > > Maybe it should be converted to code that replaces the contents instead of > replacing the *cred? (Variants of the above live in a bunch of places in the > krpc, nlm and nfs code, due to the fact that the socket functions use > td->td_ucred in various places.) td->td_ucred is a thread-local variable, meaning that it will only be accessed and modified from the current thread. So the above construct is fine. Also, struct thread should be properly aligned. :-) Robert N M Watson Computer Laboratory University of Cambridge
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