Date: Thu, 6 Aug 2009 11:39:00 -0400 (EDT) From: Rick Macklem <rmacklem@uoguelph.ca> To: Julian Elischer <julian@elischer.org> Cc: jeff@FreeBSD.org, "Bjoern A. Zeeb" <bz@FreeBSD.org>, lstewart@FreeBSD.org, freebsd-current@FreeBSD.org, kib@FreeBSD.org, Navdeep Parhar <np@FreeBSD.org>, Larry Rosenman <ler@lerctr.org>, Robert Watson <rwatson@FreeBSD.org> Subject: Re: reproducible panic in netisr Message-ID: <Pine.GSO.4.63.0908061131220.3240@muncher.cs.uoguelph.ca> In-Reply-To: <4A7AF25D.40608@elischer.org> 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> <4A7AF25D.40608@elischer.org>
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On Thu, 6 Aug 2009, Julian Elischer wrote:
> 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 krpc/nlm/nfs hack of:
>> oldcred = td->td_ucred;
>> td->td_ucred = "some other cred ptr, such as the mount one"
>> ...
>> 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.)
>
> no, creds are read-only .. you never change a cred.
> You alwasy make a new one ans use it, becasue you may be shareing your cred
> with hundreds of other sibling threads or processes. (they are refcounted)
>
Righto, yes. So does that imply that the alignment provided by crget()
{ which uses malloc() } is sufficient for td->td_ucred or is td->td_ucred
a special case?
rick
ps: The above hack, which came up in a separate discussion yesterday,
isn't gonna be easy to get rid of, imho. A whole bunch of network
related functions use td->td_ucred and the only fix I can see would
be to add "*cred" arguments to them all, so that the krpc/nlm/nfs
code could pass the correct *cred in. (It is set to the one used at
mount time for network reconnects, etc.)
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