| Message ID | 1444323427-6822-2-git-send-email-grygorii.strashko@ti.com (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
On Thursday, October 08, 2015 11:57:06 AM Grygorii Strashko wrote: > Now wait_for_device_probe() waits for currently executing probes to finish, > but it doesn't take into account deferred probing mechanism. As result, > nothing prevents deferred probe workqueue to continue probing devices right > after wait_for_device_probe() is finished. > > Hence, lest ensure deferred probe workqueue is finished in s/lest/let's/ > wait_for_device_probe() before proceeding. > > Cc: Alan Stern <stern@rowland.harvard.edu> > Cc: Rafael J. Wysocki <rjw@rjwysocki.net> > Cc: Thierry Reding <thierry.reding@gmail.com> > Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com> > --- > drivers/base/dd.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > index be0eb46..98de1a5 100644 > --- a/drivers/base/dd.c > +++ b/drivers/base/dd.c > @@ -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? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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. 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? Is the deferred_wq workqueue freezable? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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.
On Friday, October 09, 2015 09:38:13 AM Grygorii Strashko wrote: > 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. Well, in that case why don't you make it part of the second patch after all instead of making a false impression of fixing a more general problem? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 10/10/2015 12:16 AM, Rafael J. Wysocki wrote: > On Friday, October 09, 2015 09:38:13 AM Grygorii Strashko wrote: >> 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. > > Well, in that case why don't you make it part of the second patch after all > instead of making a false impression of fixing a more general problem? > ok.
diff --git a/drivers/base/dd.c b/drivers/base/dd.c index be0eb46..98de1a5 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -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();
Now wait_for_device_probe() waits for currently executing probes to finish, but it doesn't take into account deferred probing mechanism. As result, nothing prevents deferred probe workqueue to continue probing devices right after wait_for_device_probe() is finished. Hence, lest ensure deferred probe workqueue is finished in wait_for_device_probe() before proceeding. Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Rafael J. Wysocki <rjw@rjwysocki.net> Cc: Thierry Reding <thierry.reding@gmail.com> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com> --- drivers/base/dd.c | 4 ++++ 1 file changed, 4 insertions(+)