linux-kernel - Re: [rfc][patch] futex: restartable futex

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Message-ID: <20070309122417.GA15325@wotan.suse.de>
Date:	Fri, 9 Mar 2007 13:24:17 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc][patch] futex: restartable futex_wait?

On Fri, Mar 09, 2007 at 10:38:35AM +0100, Thomas Gleixner wrote:
> On Fri, 2007-03-09 at 06:10 +0100, Nick Piggin wrote:
> > > i think that's quite right. I'm wondering why this never came up before? 
> > > But your fix is not complete i think:
> > > 
> > > > +             restart->arg2 = time;
> > > > +             return -ERESTART_RESTARTBLOCK;
> > > > +     }
> > > 
> > > 'time' here is relative, so the restarted syscall will do a /full/ wait 
> > > again.
> > 
> > But it has been modified by schedule_timeout?
> 
> But this does not change the syscall registers, so it is restarted in
> the same way. We need a new futex OP for this, which takes absolute time
> like the PI futex op does.

Forgive me if I'm missing something here, but I'm using the restart block
and saving the updated value of time in ->arg2, and using that as the new
time parameter passed into futex_wait from futex_wait_restart.

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