linux-kernel - Re: [driver-core PATCH v4 4/6] driver core: Probe devices asynchronously instead of the driver

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Date:   Thu, 18 Oct 2018 13:13:56 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Cc:     len.brown@...el.com, rafael@...nel.org, linux-pm@...r.kernel.org,
        jiangshanlai@...il.com, pavel@....cz, zwisler@...nel.org,
        tj@...nel.org, akpm@...ux-foundation.org
Subject: Re: [driver-core PATCH v4 4/6] driver core: Probe devices
 asynchronously instead of the driver

On Thu, 2018-10-18 at 12:38 -0700, Alexander Duyck wrote:
> Basically if somebody loads a driver the dev->driver becomes set. If a 
> driver is removed it will clear dev->driver and set driver_data to 
> 0/NULL. That is what I am using as a mutex to track it in conjunction 
> with the device mutex. Basically if somebody attempts to attach a driver 
> before we get there we just exit and don't attempt to load this driver.

I don't think that the above matches your code. __device_attach() does not
set the dev->driver pointer before scheduling an asynchronous probe. Only
dev->driver_data gets set before the asynchonous probe is scheduled. Since
driver_detach() only iterates over devices that are in the per-driver klist
it will skip all devices for which an asynchronous probe has been scheduled
but __device_attach_async_helper() has not yet been called. My conclusion
remains that this patch does not prevent a driver pointer to become invalid
concurrently with __device_attach_async_helper() dereferencing the same
driver pointer.

Bart.