Date: Tue, 16 Nov 2010 20:31:48 -0500
From: Kyle McMartin <kyle@mcmartin.ca>
To: Mike Galbraith <efault@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups
Message-ID: <20101117013148.GA22651@bombadil.infradead.org>
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Hi Mike,

On Mon, Nov 15, 2010 at 02:25:50PM -0700, Mike Galbraith wrote:
> --- linux-2.6.orig/drivers/tty/tty_io.c
> +++ linux-2.6/drivers/tty/tty_io.c
> @@ -3160,6 +3160,7 @@ static void __proc_set_tty(struct task_s
>  	put_pid(tsk->signal->tty_old_pgrp);
>  	tsk->signal->tty = tty_kref_get(tty);
>  	tsk->signal->tty_old_pgrp = NULL;
> +	sched_autogroup_create_attach(tsk);
>  }
>  

This is a bit of a problem, as it's called in_atomic context and kmalloc's
under GFP_KERNEL (which can sleep.) This results in sleep-under-spinlock
prints when CONFIG_DEBUG_SPINLOCK_SLEEP=y.

I spent a bit of time thinking about how to fix that, but it's a bit
difficult because of the nested spin_lock_irq in that bit of the
tty_ioctl callchain.

I'll think about it some more tonight and follow-up if I can think of a
way to fix it.

regards, Kyle
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