Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH v1] PM-runtime: Check supplier_preactivated before release supplier | Date | Wed, 29 Jun 2022 18:01:35 +0200 |
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[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);
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