linux-kernel - Re: [PATCH v2 07/10] driver core: Add support for links to already probed drivers

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Date:   Wed, 07 Sep 2016 01:13:23 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org,
        linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Joerg Roedel <joro@...tes.org>,
        Inki Dae <inki.dae@...sung.com>, Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <k.kozlowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 07/10] driver core: Add support for links to already probed drivers

On Friday, June 17, 2016 08:26:57 AM Marek Szyprowski wrote:
> Set proper link state if link is created between already probed supplier
> device and to be probed consumer device.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  drivers/base/core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 4e778539b750..d9c5c5542a6b 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -125,7 +125,9 @@ struct devlink *device_link_add(struct device *consumer,
>  
>  	link->flags = flags;
>  	link->status = (flags & DEVICE_LINK_PROBE_TIME) ?
> -			DEVICE_LINK_CONSUMER_PROBE : DEVICE_LINK_DORMANT;
> +			DEVICE_LINK_CONSUMER_PROBE :
> +			(supplier->driver ? DEVICE_LINK_AVAILABLE :
> +			 DEVICE_LINK_DORMANT);
>  	spin_lock_init(&link->lock);
>  
>  	/*
> 

The supplier->driver check is insufficient and racy.

It is insufficient, because supplier->driver is also set during supplier probe
and the probe may still not be successful.

It is racy, because supplier->driver may be modified right after this check.

The only way to address the issue at hand I can see is to add a flag to
indicate to device_link_add() that the supplier has already been probed
successfully.

Thanks,
Rafael