linux-kernel - Re: [PATCH] drivercore: Add driver probe deferral mechanism

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Date:	Mon, 4 Jul 2011 12:56:55 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] drivercore: Add driver probe deferral mechanism

On Mon, 04 Jul 2011 11:11:59 -0600 Grant Likely wrote:

> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 6658da7..ccbf3d3 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -28,6 +28,62 @@
>  #include "base.h"
>  #include "power/power.h"
>  
> +/**
> + * deferred_probe_work_func() - Retry probing devices in the deferred list.
> + */
> +static DEFINE_MUTEX(deferred_probe_mutex);
> +static LIST_HEAD(deferred_probe_list);
> +static void deferred_probe_work_func(struct work_struct *work)

The kernel-doc notation needs to be immediately before the function,
without the intervening data...

> +{
> +	struct device *dev;
> +	/*
> +	 * This bit is tricky.  We want to process every device in the
> +	 * deferred list, but devices can be removed from the list at any
> +	 * time while inside this for-each loop.  There are two things that
> +	 * need to be protected against:
> +	 * - if the device is removed from the deferred_probe_list, then we
> +	 *   loose our place in the loop.  Since any device can be removed
> +	 *   asynchronously, list_for_each_entry_safe() wouldn't make things
> +	 *   much better.  Simplest solution is to restart walking the list
> +	 *   whenever the current device gets removed.  Not the most efficient,
> +	 *   but is simple to implement and easy to audit for correctness.
> +	 * - if the device is unregistered, and freed, then there is a risk
> +	 *   of a null pointer dereference.  This code uses get/put_device()
> +	 *   to ensure the device cannot disappear from under our feet.
> +	 */


---
~Randy
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