Messages in this thread | | | Subject | Re: [PATCH v1] PM-runtime: Check supplier_preactivated before release supplier | From | Peter Wang <> | Date | Thu, 30 Jun 2022 22:26:04 +0800 |
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On 6/30/22 12:01 AM, Rafael J. Wysocki wrote: > [Add CCs to linix-pm, LKML and Greg] > > On Wednesday, June 29, 2022 5:32:00 PM CEST Rafael J. Wysocki wrote: >> On Wed, Jun 29, 2022 at 4:47 PM Peter Wang <peter.wang@mediatek.com> wrote: >>> >>> On 6/29/22 9:22 PM, Rafael J. Wysocki wrote: >>>> On Wed, Jun 29, 2022 at 5:02 AM Peter Wang <peter.wang@mediatek.com> wrote: >>>>> On 6/28/22 11:54 PM, Rafael J. Wysocki wrote: >>>>>> On Tue, Jun 28, 2022 at 3:53 AM Peter Wang <peter.wang@mediatek.com> wrote: >>>>>>> On 6/28/22 3:00 AM, Rafael J. Wysocki wrote: >>>>>>>> On Mon, Jun 13, 2022 at 2:08 PM <peter.wang@mediatek.com> wrote: >>>>>>>>> From: Peter Wang <peter.wang@mediatek.com> >>>>>>>>> >>>>>>>>> With divice link of DL_FLAG_PM_RUNTIME, if consumer call pm_runtime_get_suppliers >>>>>>>>> to prevent supplier enter suspend, pm_runtime_release_supplier should >>>>>>>>> check supplier_preactivated before let supplier enter suspend. >>>>>>>> Why? >>>>>>> because supplier_preactivated is true means supplier cannot enter >>>>>>> suspend, right? >>>>>> No, it doesn't mean that. >>>>> Hi Rafael, >>>>> >>>>> if supplier_preactivated is true, means someone call >>>>> pm_runtime_get_suppliers and >>>>> before pm_runtime_put_suppliers right? This section suppliers should not >>>>> enter suspend. >>>> No, this is not how this is expected to work. >>>> >>>> First off, the only caller of pm_runtime_get_suppliers() and >>>> pm_runtime_put_suppliers() is __driver_probe_device(). Really nobody >>>> else has any business that would require calling them. >>> Hi Rafael, >>> >>> Yes, you are right! >>> __driver_probe_device the only one use and just because >>> __driver_probe_device use >>> pm_runtime_get_suppliers cause problem. >>> >>> >>>> Second, the role of pm_runtime_get_suppliers() is to "preactivate" the >>>> suppliers before running probe for a consumer device and the role of >>> the role of pm_runtime_get_suppliers() is to "preactivate" the suppliers, >>> but suppliers may suspend immediately after preactivate right? >>> Here is just this case. this is first racing point. >>> Thread A: pm_runtime_get_suppliers -> __driver_probe_device >>> Thread B: pm_runtime_release_supplier >>> Thread A: Run with supplier not preactivate -> __driver_probe_device >>> >>>> pm_runtime_put_suppliers() is to do the cleanup in case the device is >>>> left in suspend after probing. >>>> >>>> IOW, pm_runtime_get_suppliers() is to ensure that the suppliers will >>>> be active until the probe callback takes over and the rest depends on >>>> that callback. >>> The problem of this racing will finally let consumer is active but >>> supplier is suspended. >> So it would be better to send a bug report regarding this. >> >>> The link relation is broken. >>> I know you may curious how it happened? right? >>> Honestly, I am not sure, but I think the second racing point >>> is rpm_get_suppliers and pm_runtime_put_suppliers(release rpm_active). >> I'm not sure what you mean by "the racing point". >> >> Yes, these functions can run concurrently. >> >>> So, I try to fix the first racing point and the problem is gone. >>> It is full meet expect, and the pm runtime will work smoothly after >>> __driver_probe_device done. >> I'm almost sure that there is at least one scenario that would be >> broken by this change. > That said, the code in there may be a bit overdesigned. > > Does the patch below help? > > --- > drivers/base/power/runtime.c | 14 +------------- > 1 file changed, 1 insertion(+), 13 deletions(-) > > Index: linux-pm/drivers/base/power/runtime.c > =================================================================== > --- linux-pm.orig/drivers/base/power/runtime.c > +++ linux-pm/drivers/base/power/runtime.c > @@ -1768,7 +1768,6 @@ void pm_runtime_get_suppliers(struct dev > if (link->flags & DL_FLAG_PM_RUNTIME) { > link->supplier_preactivated = true; > pm_runtime_get_sync(link->supplier); > - refcount_inc(&link->rpm_active); > } > > device_links_read_unlock(idx); > @@ -1788,19 +1787,8 @@ void pm_runtime_put_suppliers(struct dev > list_for_each_entry_rcu(link, &dev->links.suppliers, c_node, > device_links_read_lock_held()) > if (link->supplier_preactivated) { > - bool put; > - > link->supplier_preactivated = false; > - > - spin_lock_irq(&dev->power.lock); > - > - put = pm_runtime_status_suspended(dev) && > - refcount_dec_not_one(&link->rpm_active); > - > - spin_unlock_irq(&dev->power.lock); > - > - if (put) > - pm_runtime_put(link->supplier); > + pm_runtime_put(link->supplier); > } > > device_links_read_unlock(idx);
Hi Rafael,
I think this patch solve the rpm_active racing problem. But it still have problem that pm_runtime_get_suppliers call pm_runtime_get_sync(link->supplier) and supplier could suspend immediately by other thread who call pm_runtime_release_supplier.
Thanks. Peter
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