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From: Rusty Russell <rusty@rustcorp.com.au>
To: frankeh@watson.ibm.com
Cc: davidel@xmailserver.org, rml@tech9.net, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Fast Userspace Mutexes III. 
In-Reply-To: Your message of "Tue, 05 Mar 2002 10:15:44 CDT."
             <20020305151439.457E03FE06@smtp.linux.ibm.com> 
Date: Wed, 06 Mar 2002 12:31:01 +1100
Message-Id: <E16iQGk-0005ds-00@wagner.rustcorp.com.au>
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In message <20020305151439.457E03FE06@smtp.linux.ibm.com> you write:
> I agree to put it there if its not used as a means to define whether
> user locks are permitted or not. If that is the intention, then the current 
> futex will need to check every access through find_vma(), which we
> both know nobody wants to do.
> 
> So it can only be used for architectural hints, agreed ?

Yes.  It *might* work if you don't PROT_SEM the page the semaphore is
on, but it's still a bug waiting to happen.  OTOH, it'd be nice if
PROT_SEM returns EINVAL was a reliably indicator of no futex support.
This way you actually need to call the futex syscall once to see if it
works.

Cheers!
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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