Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

[Kyle McMartin]

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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