From owner-freebsd-arch  Fri Feb 22 11:41: 0 2002
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Date: Fri, 22 Feb 2002 11:34:48 -0800 (PST)
From: Julian Elischer <julian@elischer.org>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: John Baldwin <jhb@FreeBSD.ORG>, arch@FreeBSD.ORG
Subject: Re: RE: that INVARIANT/ucred freeing stuff.
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On Fri, 22 Feb 2002, Matthew Dillon wrote:

>     Sigh.  Well, if you really want.  I don't like the idea of
>     the size of the thread structure changing just due to someone
>     turning on or off DIAGNOSTIC though.
> 

I'LL JUST THROW IN A DUMMY (Geez, bloody capslock)..

> 						-Matt
> 
> :OK here is my suggestion:
> :
> :We add extra code under DIAGNOSTIC
> :the code does:
> :
> :in proc.h
> :
> :add a field to thread of:
> :#ifdef DIAGNOSTIC
> :	td_ucred_cache
> :#endif /* DIAGNOSTIC */
> :
> :
> :on texiting the kernel:
> :
> :#ifdef DIAGNOSTIC
> :	if (td->td_ucred_cache)
> :		panic("thread already has cached ucred");
> :	td->td_ucred_cache = td->td_ucred;
> :	td->td_ucred = NULL;
> :#endif /* DIAGNOSTIC */
> :
> :
> :on entering the kernel we do:
> :
> :
> :#ifdef DIAGNOSTIC
> :	if (td->td_ucred)
> :		panic("thread got a cred form somewhere in userspace");
> :	td->td_cred = td->td_ucred_cache;
> :	td->td_ucred_cache = NULL;
> :#endif /* DIAGNOSTIC */
> :	if (td->ucred != p->p_ucred)
> :		cred_update_thread(td);
> :
> :we get good performance even when it it is optionned in and 
> :still have a NULL ucred pointer when in user space when DIAGNOSTIC
> :is turned on. With no DIAGNOSTICS we get the best performance,
> :and don't even bother to shift the reference.
> 
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