linux-kernel - Re: Stupid futex question

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Message-ID: <1266512486.26719.856.camel@laptop>
Date:	Thu, 18 Feb 2010 18:01:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Valdis.Kletnieks@...edu
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Stupid futex question - 2.6.33-rc7-mmotm0210

On Thu, 2010-02-18 at 11:42 -0500, Valdis.Kletnieks@...edu wrote:

> 1) should it get killed for RLIMIT_RTTIME because it's been in a futex()
> for multiple seconds? It seems suspicious - docs say a blocking syscall
> resets RTTIME - so if futex() blocks it shouldn't kill, and if it's in the
> kernel for a second without blocking it's a bug too.

sys_futex() shouldn't be taking that long indeed, and if its not caused
by the sysrq interrupt then something funny is going on indeed.

You could poke around in kernel/futex.c:futex_wait() to see where it
thinks its spending it time? There's a single retry loop in there, maybe
instrument that to see if its retrying too many times..

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