Re: [RFC PATCH 2/3] PM / Runtime: force memory allocation with noI/O during runtime_resume callbcack

[Alan Stern]

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@xxxxxxxxxxxxxxxxxxx>
> Cc: Oliver Neukum <oneukum@xxxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> ---
>  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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/