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

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Message-ID: <20070308172902.GA16834@elte.hu>
Date:	Thu, 8 Mar 2007 18:29:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [rfc][patch] futex: restartable futex_wait?


* Nick Piggin <npiggin@...e.de> wrote:

> Hi Ingo,
> 
> I'm seeing an LTP test fail for ltp test sigaction_16_24. Basically, 
> it tests whether the SA_RESTART flag works for the sem_wait operation.
> 
> I see sem_wait is implemented with futex_wait, so I wonder whether we 
> can make it restartable? Am I going about it the right way? (Seems to 
> fix the testcase here).

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.

maybe we should rather convert futex timed-waits to hrtimers? Thomas?

	Ingo
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