linux-kernel - Re: [PATCH v1 1/5] drivercore: Revert "deferral race condition fix"

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Date:   Sat, 10 Nov 2018 10:26:22 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        linux-usb@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Roger Quadros <rogerq@...com>, linux-pm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sebastian Reichel <sre@...nel.org>, linux-omap@...r.kernel.org,
        Darren Hart <dvhart@...radead.org>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chen-Yu Tsai <wens@...e.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Grant Likely <grant.likely@...aro.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Mark Brown <broonie@...nel.org>,
        Andrzej Hajda <a.hajda@...sung.com>
Subject: Re: [PATCH v1 1/5] drivercore: Revert "deferral race condition fix"

On Sat, Nov 10, 2018 at 08:10:57PM +0200, Andy Shevchenko wrote:
> Consider the following scenario.
> 
> There are two independent devices coupled together by functional dependencies:
>  - USB OTG (dwc3-pci)
>  - extcon (tested with extcon-intel-mrfld, not yet in upstream)
> 
> Each of the driver services a corresponding device is built as a module. In the
> Buildroot environment the modules are probed by alphabetical ordering of their
> modaliases. The latter comes to the case when USB OTG driver will be probed
> first followed by extcon one.
> 
> So, if the platform anticipates extcon device to be appeared, in the above case
> we will get deferred probe of USB OTG, because of ordering.
> 
> Now, a cherry on top of the cake, the deferred probing list contains
> the only two modules, i.e. USB OTG and extcon. Due to above circumstances,
> values in the local_trigger_count and deferred_trigger_count are not the same,
> and thus provokes deferred probe triggering again and again.
> 
> ...
> [   20.678332] platform dwc3.0.auto: Retrying from deferred list
> [   20.694743] platform dwc3.0.auto: Driver dwc3 requests probe deferral
> [   20.701254] platform dwc3.0.auto: Added to deferred list
> [   20.706620] platform dwc3.0.auto: driver_deferred_probe_add_trigger 1 2
> [   20.713732] platform dwc3.0.auto: Retrying from deferred list
> [   20.730035] platform dwc3.0.auto: Driver dwc3 requests probe deferral
> [   20.736540] platform dwc3.0.auto: Added to deferred list
> [   20.741889] platform dwc3.0.auto: driver_deferred_probe_add_trigger 3 4
> [   20.748991] platform dwc3.0.auto: Retrying from deferred list
> [   20.765416] platform dwc3.0.auto: Driver dwc3 requests probe deferral
> [   20.771914] platform dwc3.0.auto: Added to deferred list
> [   20.777279] platform dwc3.0.auto: driver_deferred_probe_add_trigger 5 6
> ...
> 
> Deeper investigation shows the culprit commit 58b116bce136
> ("drivercore: deferral race condition fix") which was dedicated to fix some
> other issue while bringing a regression.
> 
> This reverts commit 58b116bce13612e5aa6fcd49ecbd4cf8bb59e835 for good until
> we will have better solution.
> 
> Cc: Grant Likely <grant.likely@...aro.org>
> Cc: Peter Ujfalusi <peter.ujfalusi@...com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Felipe Balbi <balbi@...nel.org>
> Cc: Andrzej Hajda <a.hajda@...sung.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/base/dd.c | 27 ++-------------------------
>  1 file changed, 2 insertions(+), 25 deletions(-)

Shouldn't there be a "Fixes:" line and cc: stable here?

thanks,

greg k-h