linux-kernel - Re: [ckrm-tech] [PATCH 4/13] BC: context handling

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Message-ID: <6599ad830611230131w1bf63dc1m1998b55b61579509@mail.gmail.com>
Date:	Thu, 23 Nov 2006 01:31:47 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Pavel Emelianov" <xemul@...nvz.org>
Cc:	"Kirill Korotaev" <dev@...ru>, "Andrew Morton" <akpm@...l.org>,
	ckrm-tech@...ts.sourceforge.net,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	matthltc@...ibm.com, hch@...radead.org,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>, oleg@...sign.ru,
	devel@...nvz.org
Subject: Re: [ckrm-tech] [PATCH 4/13] BC: context handling

On 11/23/06, Pavel Emelianov <xemul@...nvz.org> wrote:
> You mean moving is like this:
>
> old_bc = task->real_bc;
> task->real_bc = new_bc;
> cmpxchg(&tsk->exec_bc, old_bc, new_bc);
>
> ? Then this won't work:
>
> Initialisation:
> current->exec_bc = init_bc;
> current->real_bc = init_bc;
> ...
> IRQ:
> current->exec_bc = init_bc;
> ...
>                              old_bc = tsk->real_bc; /* init_bc */
>                              tsk->real_bc = bc1;
>                              cx(tsk->exec_bc, init_bc, bc1); /* ok */
> ...
> Here at the middle of an interrupt
> we have bc1 set as exec_bc on task
> which IS wrong!

You could get round that by having a separate "irq_bc" that's never
valid for a task not in an interrupt.

Paul
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