reproducible panic in netisr

Julian Elischer julian at
Thu Aug 6 15:10:23 UTC 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.)

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 

> rick
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