On 04/08/2014 03:47 PM, Grant Likely wrote: > On Tue, Apr 8, 2014 at 3:27 AM, Grant Likely <grant.lik...@secretlab.ca> > wrote: >> On Thu, 3 Apr 2014 10:40:59 +0100, Mark Brown <broo...@kernel.org> wrote: >>> On Thu, Apr 03, 2014 at 10:12:07AM +0300, Peter Ujfalusi wrote: >>>> When the kernel is built with CONFIG_PREEMPT it is possible to reach a >>>> state >>>> when all modules loaded but some driver still stuck in the deferred list >>>> and there is a need for external event to kick the deferred queue to probe >>>> these drivers. >>> >>> Acked-by: Mark Brown <broo...@linaro.org> >> >> It's a pretty crude solution though. The problem is any "in-flight" >> probes that are going to defer will not get added to the active list. >> Rerunning the entire active list is a bit much (but it does have the >> advantage of still being conceptually simple). I think we can do better. >> >> Instead of running the entire list, we could add a check to >> driver_deferred_probe_add() that adds the device to the active list >> instead of pending list on the condition that another driver probe >> completed while the deferred probe was in-flight. >> >> I'm playing with a solution now. I'll email a proposal shortly. > > Thinking out loud now... > > The race can occur whenever a probe in another thread completes > successfully while the current probe is in-flight. If that has > happened, then the defer condition may be resolved and the driver > should be scheduled for retry immediately. If the core code can check > for that condition, then we can add the driver directly to the active > list and kick the workqueue. > > The problem is that we don't currently have an easy way to test if a > probe has completed in another thread. This patch handles it with a > single flag that gets set whenever a probe completes while another > probe is executing. I was worried that this approach would be racy, > but after running through the scenarios I can't find a situation where > it wouldn't get added. I only concern I have remaining on this > approach is that it will trigger unnecessary retries, but even that > isn't really a problem because the pending list will have been moved > to the active list *anyway*. It isn't even a retry of the whole list > that's happening because most likely the only device on the pending > list will be the one that completed with -EPROBE_DEFER.
This code will only going to add one retry and it is going to that only under the condition you have described: the last driver which finishes it's probe ends up with -EPROBE_DEFER and while it's probe was in-flight another driver loaded with success. In all other cases this will not trigger a retry: If you load only one driver which ends up deferring, If the driver which differing is not the last driver to load - since we will have other drivers to be loaded and they will kick the list anyways. > So, I actually think this is the right approach now. I'll reply to the > patch itself and make some comments on the code. Thanks, I'll check the comments. -- Péter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/