From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grygorii Strashko Subject: Re: [PATCH 1/2] PM / sleep: ensure deferred probe workqueue is finished in wait_for_device_probe Date: Fri, 9 Oct 2015 09:38:13 -0500 Message-ID: <5617D155.60700@ti.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: Received: from bear.ext.ti.com ([192.94.94.41]:46744 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755891AbbJIOiV (ORCPT ); Fri, 9 Oct 2015 10:38:21 -0400 In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Alan Stern , "Rafael J. Wysocki" Cc: Greg Kroah-Hartman , Pavel Machek , Len Brown , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Thierry Reding On 10/08/2015 03:53 PM, Alan Stern wrote: > On Thu, 8 Oct 2015, Rafael J. Wysocki wrote: > >>> @@ -391,6 +391,10 @@ int driver_probe_done(void) >>> */ >>> void wait_for_device_probe(void) >>> { >>> + /* wait for the deferred probe workqueue to finish */ >>> + if (driver_deferred_probe_enable) >>> + flush_workqueue(deferred_wq); >>> + >>> /* wait for the known devices to complete their probing */ >>> wait_event(probe_waitqueue, atomic_read(&probe_count) == 0); >>> async_synchronize_full(); >> >> I'm not sure if this is sufficient. >> >> Something may be added to the workqueue right after you've flushed it and >> then be reporobed after the wait_event() in theory. Or am I missing anything? > > Maybe I'm missing part of this, but I think the point is to make sure > that every probe which began or was queued before this function got > called, has finished before the function returns. > > Thus, in the case at hand we want to defer all probes starting from > some point in the system sleep transition. Grygorii sets his > defer_all_probes variable and then calls this function. It waits for > any probes that were initiated before the function call. Any probe > that was initiated after the function call (for example, the ones > you're concerned about between the flush_workqueue and wait_event) will > see that defer_all_probes is set and so will defer itself. Yes. It will work as expected with the next patch. For all other case, where this API is used alone - it will make things more safe, but there is no way to completely block scheduling of new probes. > > Now, I'm not sure what happens when a probe that was deferred tries to > defer itself again. Do we end up in an infinite probing loop? No. handling of defered probes will be re triggered only if some probe was finished successfully. > Is the deferred_wq workqueue freezable? seems WQ_FREEZABLE is not set for this WQ. -- regards, -grygorii