linux-kernel - Re: syscall_regfunc() && TIF_SYSCALL

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Message-ID: <1333152806.23924.196.camel@gandalf.stny.rr.com>
Date:	Fri, 30 Mar 2012 20:13:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...hat.com>, Jason Baron <jbaron@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: syscall_regfunc() && TIF_SYSCALL_TRACEPOINT

On Fri, 2012-03-30 at 22:15 +0200, Oleg Nesterov wrote:

> > A lot of places test ->mm for kernel threads.
> 
> And this is wrong, use_mm() can set ->mm != NULL. This is the common
> mistake.
> 
> > Just search for ->mm in
> > kernel/sched/core.c
> 
> Probably normalize_rt_tasks() and __sched_setscheduler() should be fixed.

Heh, the __sched_setscheduler() usage is from me. But I'm not sure we
had an alternative back in 2005.


> But I don't really understand why do you think that "clear" is more
> important.

They are both important. But as I tend to consider performance when
tracing is off as critical, I'm more concerned about that. But both must
be fixed, because not reporting traces can confuse a developer.



>  Sure, the wrong TIF_SYSCALL_TRACEPOINT triggers the slow
> path unnecessary, but this is more or less harmless. But if we do
> not set the task obviously won't report trace_sys*, this looks like
> a bug even if nothing bad can happen.

Agreed, both are a bug and both should be fixed.

Thanks,

-- Steve


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