linux-kernel - Re: [PATCH -rt] rt-slab: fix cpu inconsistency case

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Message-ID: <Pine.LNX.4.58.0803241639220.9884@gandalf.stny.rr.com>
Date:	Mon, 24 Mar 2008 16:40:43 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH -rt] rt-slab: fix cpu inconsistency case


On Mon, 24 Mar 2008, Steven Rostedt wrote:

>
> On Fri, 21 Mar 2008, Hiroshi Shimamoto wrote:
> >
> > >
> > > Is this a bug in mainline? The !PREEMPT_RT case should be as close to
> > > mainline as possible, with no actual changes in object code. If this is
> > > not the case, then we need to fix that.
> >
> > No, this issue is in -rt only.
> >
>
> Hi Hiroshi,
>
> Thanks again for reporting this. I took a deeper look into this today and
> came to the conclusion that we need to get rid of both
> slab_irq_disable_nort and slab_irq_disable_rt, and simply use
> slab_irq_disable ;-)
>
> This is what you patch indirectly does. I'll write up another patch to fix
> this.
>

Actually, I'm going to take your patch.

Seems that the reason Ingo did the two separate, is that the functions
called also call the slab_irq_save, which will retake the locks in
PREEMPT_RT. If we don't release the lock, then we can deadlock.

Thanks,

-- Steve

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