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

Greg Kroah-Hartman
2018-11-10T18:26:22Z

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@linaro.org>
> Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Felipe Balbi <balbi@kernel.org>
> Cc: Andrzej Hajda <a.hajda@samsung.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.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