linux-kernel - Re: [PATCH] drivers/base: stop new probing during shutdown

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Date:   Thu, 19 Jul 2018 10:07:18 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] drivers/base: stop new probing during shutdown

On Thursday, July 19, 2018 7:14:58 AM CEST Pingfan Liu wrote:
> There is a race window in device_shutdown(), which may cause
> -1. parent device shut down before child or
> -2. no shutdown on a new probing device.
> 
> For 1st, taking the following scenario:
>          device_shutdown                        new plugin device
>   list_del_init(parent_dev);
>   spin_unlock(list_lock);
>                                                   device_add(child)
>                                                   probe child
>   shutdown parent_dev
>        --> now child is on the tail of devices_kset
> 
> For 2nd, taking the following scenario:
>          device_shutdown                        new plugin device
>                                                   device_add(dev)
>   device_lock(dev);
>   ...
>   device_unlock(dev);
>                                                   probe dev
>        --> now, the new occurred dev has no opportunity to shutdown
> 
> To fix this race issue, just prevent the new probing request. With this
> logic, device_shutdown() is more similar to dpm_prepare().

Right.

This still doesn't prevent new children of a device from being added during
shutdown (something like the PM ->prepare callback would be needed for that),
but at least it prevents drivers from binding to the new devices.

Reviewed-by: Rafael J. Wysocki <rafael@...nel.org>

> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> ---
>  drivers/base/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index df3e1a4..3aba4ad 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2809,6 +2809,9 @@ void device_shutdown(void)
>  {
>  	struct device *dev, *parent;
>  
> +	wait_for_device_probe();
> +	device_block_probing();
> +
>  	spin_lock(&devices_kset->list_lock);
>  	/*
>  	 * Walk the devices list backward, shutting down each in turn.
>