linux-kernel - Re: second, bigger problem with private futexes

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Message-ID: <4651E992.9080205@cosmosbay.com>
Date:	Mon, 21 May 2007 20:48:50 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Ulrich Drepper <drepper@...hat.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: second, bigger problem with private futexes

Ulrich Drepper a écrit :
> -----BEGIN PGP SIGNED MESSAGE-----
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> 
> Eric Dumazet wrote:
>> Do you mean POSIX allowed to mix PROCESS_PRIVATE and PROCESS_SHARED
>> condvar and mutexes ? Seems silly to me :(
> 

> Don't judge what you don't understand.

Yes, I kindly apologise for this crime.

 > If all waiters are always in one
> process but the notifiers can be in different processes, this setup
> might make a lot of sense.

Thanks for providing this information.

I assume in this case the condvar is PSHARED, while mutex could be/is PRIVATE ?

I wonder how old (assuming all shared) code could work, since the notifier 
would call FUTEX_CMP_REQUEUE giving a target address outside of this process vm ?

My understanding (probably bad, since I know nothing about POSIX as you mentioned)

- Old code could not use FUTEX_CMP_REQUEUE if mutex was private.
-> Old code was using a normal FUTEX_WAKE in this case.

So I repeat my question : Should we really add yer another futex command in 
kernel for a corner case ?

Thanks
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