linux-kernel - Re: sys_rt_sigreturn calling sys

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Message-ID: <alpine.LFD.2.00.1001222257480.2906@localhost.localdomain>
Date:	Fri, 22 Jan 2010 23:00:15 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ivan Novick <novickivan@...il.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: sys_rt_sigreturn calling sys_futex?

On Fri, 22 Jan 2010, Ivan Novick wrote:
> Hello,
> 
> I have a userspace app that I profiled using SystemTap.
> 
> It says there are frequent calls to sys_futex which come from sys_rt_sigreturn.
> 
> It is true, that my app has many signal handler calls due to
> frequently set timers in the code.
> 
> I had a look at the source for my kernel: Suse: linux-2.6.27.39-0.3
> but I don't see any calls to futex from inside sys_rt_sigreturn.
> 
> Do you know if sys_rt_sigreturn is somehow calling sys_futex?

Well, it is not calling sys_futex, it is resuming the sys_futex
syscall which was interrupted by the signal. When the signal handler
returns it returns to the system call automatically.

Thanks,

	tglx
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