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

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Message-ID: <1e061fe5-9be4-77be-5350-4cb7175afdf8@acm.org>
Date:   Thu, 18 Oct 2018 19:31:12 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     alexander.h.duyck@...ux.intel.com,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>, len.brown@...el.com,
        rafael@...nel.org, linux-pm@...r.kernel.org,
        jiangshanlai@...il.com, pavel@....cz, zwisler@...nel.org,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [driver-core PATCH v4 4/6] driver core: Probe devices
 asynchronously instead of the driver

On 10/18/18 7:20 PM, Alexander Duyck wrote:
> I see what you are talking about now. Actually I think this was an
> existing issue before my patch even came into play. Basically the code
> as it currently stands is device specific in terms of the attach and
> release code.
> 
> I wonder if we shouldn't have the async_synchronize_full call in
> __device_release_driver moved down and into driver_detach before we
> even start the for loop. Assuming the driver is no longer associated
> with the bus that should flush out all devices so that we can then
> pull them out of the devices list at least. I may look at adding an
> additional bitflag to the device struct to indicate that it has a
> driver attach pending. Then for things like races between any attach
> and detach calls the logic becomes pretty straight forward. Attach
> will set the bit and provide driver data, detach will clear the bit
> and the driver data. If a driver loads in between it should clear the
> bit as well.
> 
> I'll work on it over the next couple days and hopefully have something
> ready for testing/review early next week.

Hi Alex,

How about checking in __driver_attach_async_helper() whether the driver 
pointer is still valid by checking whether bus_for_each_drv(dev->bus, 
...) can still find the driver pointer? That approach requires 
protection with a mutex to avoid races with the driver detach code but 
shouldn't require any new flags in struct device.

Thanks,

Bart.