linux-kernel - Re: Filesystem lockup with CONFIG_PREEMPT

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Message-ID: <1403892474.5830.41.camel@marge.simpson.net>
Date:	Fri, 27 Jun 2014 20:07:54 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Austin Schuh <austin@...oton-tech.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Weinberger <richard.weinberger@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: Filesystem lockup with CONFIG_PREEMPT_RT

On Fri, 2014-06-27 at 13:54 -0400, Steven Rostedt wrote: 
> On Fri, 27 Jun 2014 19:34:53 +0200
> Mike Galbraith <umgwanakikbuti@...il.com> wrote:
> 
> > On Fri, 2014-06-27 at 10:01 -0400, Steven Rostedt wrote:
> > 
> > > This seems like a lot of hacks.
> > 
> > It is exactly that, lacking proper pooper-scooper, show rt kernel how to
> > not step in it.
> > 
> > > I'm wondering if it would work if we
> > > just have the rt_spin_lock_slowlock not call schedule(), but call
> > > __schedule() directly. I mean it would keep with the mainline paradigm
> > > as spinlocks don't sleep there, and one going to sleep in the -rt
> > > kernel is similar to it being preempted by a very long NMI.
> > 
> > Problem being that we do sleep there, do need wakeup.  I have a hack
> > that turns them back into spinning locks, but it.. works too :)
> 
> Why do we need the wakeup? the owner of the lock should wake it up
> shouldn't it?

True, but that can take ages.

-Mike 

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