linux-kernel - Re: [PATCH] driver core: flush async calls before testing driver removal

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Date:   Sat, 10 Dec 2016 14:38:41 +0200
From:   Vladimir Zapolskiy <vz@...ia.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: flush async calls before testing driver
 removal

Hello Greg,

On 12/10/2016 09:32 AM, Greg Kroah-Hartman wrote:
> On Sat, Dec 10, 2016 at 02:15:19AM +0200, Vladimir Zapolskiy wrote:
>> If CONFIG_DEBUG_TEST_DRIVER_REMOVE option is enabled a number of false
>> positives are reported for ATA controller drivers, because ATA port
>> probes are done asynchronously, and the same problem may also touch
>> other asynchronously probed drivers.
>>
>> To reduce the rate of false reports on boot call async_synchronize_full()
>> before attempting to remove a driver, the same is done in delete_module()
>> syscall for all possible drivers and in __device_release_driver() function
>> for asynchronously probed drivers.
> 
> __device_release_driver() already calls this function, why call it
> again?
> 

__device_release_driver() is not called on test removal of drivers, if
CONFIG_DEBUG_TEST_DRIVER_REMOVE option is enabled.

This opens a possibility to races like one I've discovered:

  https://www.spinics.net/lists/linux-ide/msg53473.html

Next, async_synchronize_full() from __device_release_driver() is not
called in case of removal of ATA controller drivers, because
driver_allows_async_probing(drv) return value is false.

--
With best wishes,
Vladimir