linux-kernel - Re: [RFC PATCH 2/3] PM / Runtime: force memory allocation with no I/O during runtime

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Date:	Mon, 15 Oct 2012 10:14:35 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <ming.lei@...onical.com>
cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	Oliver Neukum <oneukum@...e.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [RFC PATCH 2/3] PM / Runtime: force memory allocation with no
 I/O during runtime_resume callbcack

On Mon, 15 Oct 2012, Ming Lei wrote:

> This patch applies the introduces tsk_memalloc_forbid_io() and
> tsk_memalloc_allow_io() to force memory allocation with no I/O
> during runtime_resume callback.
> 
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: Oliver Neukum <oneukum@...e.de>
> Cc: Rafael J. Wysocki <rjw@...k.pl>
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
>  drivers/base/power/runtime.c |   13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 3148b10..76836c1 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -652,7 +652,20 @@ static int rpm_resume(struct device *dev, int rpmflags)
>  	if (!callback && dev->driver && dev->driver->pm)
>  		callback = dev->driver->pm->runtime_resume;
>  
> +	/*
> +	 * Deadlock might be caused if memory allocation with GFP_KERNEL
> +	 * happens inside runtime_resume callback of one block device's
> +	 * ancestor or the block device itself. The easiest approach is
> +	 * to forbid I/O inside runtime_resume of all devices.
> +	 *
> +	 * In fact, it can be done only if the deivce is a block device
> +	 * or there is one block device descendant. But that may become
> +	 * complicated and not efficient because device tree traversing
> +	 * is involved.
> +	 */
> +	tsk_memalloc_forbid_io(current);
>  	retval = rpm_callback(callback, dev);
> +	tsk_memalloc_allow_io(current);

This is not so good.  What happens if I/O was already forbidden when
this function was called?

Alan Stern

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