[v1] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

[PATCH] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

Posted by Pin-yen Lin 3 weeks, 2 days ago

Device links with DL_FLAG_SYNC_STATE_ONLY should not affect suspend
and resume, and functions like device_reorder_to_tail() and
device_link_add() doesn't try to reorder the consumers with such flag.

However, dpm_wait_for_consumers() and dpm_wait_for_suppliers() doesn't
check this flag before triggering dpm_wait, leading to potential hang
during suspend/resume.

Add DL_FLAG_SYNC_STATE_ONLY in dpm_wait_for_consumers() and
dpm_wait_for_suppliers() to fix this.

Fixes: 05ef983e0d65a ("driver core: Add device link support for SYNC_STATE_ONLY flag")
Signed-off-by: Pin-yen Lin <treapking@chromium.org>
---

 drivers/base/power/main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 2ea6e05e6ec90..3271f4af2cb65 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -282,7 +282,8 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
 	 * walking.
 	 */
 	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
-		if (READ_ONCE(link->status) != DL_STATE_DORMANT)
+		if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
+		    !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))
 			dpm_wait(link->supplier, async);
 
 	device_links_read_unlock(idx);
@@ -339,7 +340,8 @@ static void dpm_wait_for_consumers(struct device *dev, bool async)
 	 * unregistration).
 	 */
 	list_for_each_entry_rcu_locked(link, &dev->links.consumers, s_node)
-		if (READ_ONCE(link->status) != DL_STATE_DORMANT)
+		if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
+		    !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))
 			dpm_wait(link->consumer, async);
 
 	device_links_read_unlock(idx);
-- 
2.51.0.384.g4c02a37b29-goog

Re: [PATCH] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

Posted by Rafael J. Wysocki 3 weeks, 1 day ago

On Tue, Sep 9, 2025 at 11:44 AM Pin-yen Lin <treapking@chromium.org> wrote:
>
> Device links with DL_FLAG_SYNC_STATE_ONLY should not affect suspend
> and resume, and functions like device_reorder_to_tail() and
> device_link_add() doesn't try to reorder the consumers with such flag.
>
> However, dpm_wait_for_consumers() and dpm_wait_for_suppliers() doesn't
> check this flag before triggering dpm_wait, leading to potential hang
> during suspend/resume.

Have you seen this happen or is it just a theory?

> Add DL_FLAG_SYNC_STATE_ONLY in dpm_wait_for_consumers() and
> dpm_wait_for_suppliers() to fix this.

The above sentence is incomplete AFAICS.

> Fixes: 05ef983e0d65a ("driver core: Add device link support for SYNC_STATE_ONLY flag")
> Signed-off-by: Pin-yen Lin <treapking@chromium.org>
> ---
>
>  drivers/base/power/main.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 2ea6e05e6ec90..3271f4af2cb65 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -282,7 +282,8 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
>          * walking.
>          */
>         list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
> -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> +                   !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))

This should use a check like device_link_flag_is_sync_state_only(),
which is different from the above one, for consistency with
device_reorder_to_tail().

>                         dpm_wait(link->supplier, async);
>
>         device_links_read_unlock(idx);
> @@ -339,7 +340,8 @@ static void dpm_wait_for_consumers(struct device *dev, bool async)
>          * unregistration).
>          */
>         list_for_each_entry_rcu_locked(link, &dev->links.consumers, s_node)
> -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> +                   !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))

And same here.

>                         dpm_wait(link->consumer, async);
>
>         device_links_read_unlock(idx);
> --

Re: [PATCH] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

Posted by Pin-yen Lin 3 weeks, 1 day ago

Hi Rafael,

Thanks for the review.

On Wed, Sep 10, 2025 at 7:56 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Tue, Sep 9, 2025 at 11:44 AM Pin-yen Lin <treapking@chromium.org> wrote:
> >
> > Device links with DL_FLAG_SYNC_STATE_ONLY should not affect suspend
> > and resume, and functions like device_reorder_to_tail() and
> > device_link_add() doesn't try to reorder the consumers with such flag.
> >
> > However, dpm_wait_for_consumers() and dpm_wait_for_suppliers() doesn't
> > check this flag before triggering dpm_wait, leading to potential hang
> > during suspend/resume.
>
> Have you seen this happen or is it just a theory?

We initially see this with a downstream kernel, but I can reproduce
this with the upstream kernel when I connect the usb host controller
to a "usb-a-connector" node on MT8186 Corsola Chromebook. The
devicetree looks like:

usb-a-connector {
        compatible = "usb-a-connector";
        port {
                usb_a_con: endpoint {
                        remote-endpoint = <&usb_hs>;
                };
        };
};

usb_host {
        compatible = "mediatek,mt8186-xhci", "mediatek,mtk-xhci";
        port {
                usb_hs: endpoint {
                        remote-endpoint = <&usb_a_con>;
                };
        };
};

In this case, the two nodes form a cycle and I ended up seeing a
SYNC_STATE_ONLY devlink from usb_host (supplier) to the
usb-a-connector (consumer).

I'm not very sure why we didn't see this issue before. Maybe it's
related to the fact that the usb-a-connector has a compatible string
(so a platform device is created) but no driver binds into it.
>
> > Add DL_FLAG_SYNC_STATE_ONLY in dpm_wait_for_consumers() and
> > dpm_wait_for_suppliers() to fix this.
>
> The above sentence is incomplete AFAICS.

Sorry, I meant "Add a check for DL_FLAG_SYNC_STATE_ONLY in ...". I'll
update this in the next version.
>
> > Fixes: 05ef983e0d65a ("driver core: Add device link support for SYNC_STATE_ONLY flag")
> > Signed-off-by: Pin-yen Lin <treapking@chromium.org>
> > ---
> >
> >  drivers/base/power/main.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index 2ea6e05e6ec90..3271f4af2cb65 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -282,7 +282,8 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
> >          * walking.
> >          */
> >         list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
> > -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> > +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> > +                   !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))
>
> This should use a check like device_link_flag_is_sync_state_only(),
> which is different from the above one, for consistency with
> device_reorder_to_tail().

Thanks. I'll fix this in the next version.
>
> >                         dpm_wait(link->supplier, async);
> >
> >         device_links_read_unlock(idx);
> > @@ -339,7 +340,8 @@ static void dpm_wait_for_consumers(struct device *dev, bool async)
> >          * unregistration).
> >          */
> >         list_for_each_entry_rcu_locked(link, &dev->links.consumers, s_node)
> > -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> > +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> > +                   !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))
>
> And same here.
>
> >                         dpm_wait(link->consumer, async);
> >
> >         device_links_read_unlock(idx);
> > --

Regards,
Pin-yen

Re: [PATCH] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

Posted by Rafael J. Wysocki 3 weeks, 1 day ago

Hi,

On Wed, Sep 10, 2025 at 2:43 PM Pin-yen Lin <treapking@chromium.org> wrote:
>
> Hi Rafael,
>
> Thanks for the review.
>
> On Wed, Sep 10, 2025 at 7:56 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Tue, Sep 9, 2025 at 11:44 AM Pin-yen Lin <treapking@chromium.org> wrote:
> > >
> > > Device links with DL_FLAG_SYNC_STATE_ONLY should not affect suspend
> > > and resume, and functions like device_reorder_to_tail() and
> > > device_link_add() doesn't try to reorder the consumers with such flag.
> > >
> > > However, dpm_wait_for_consumers() and dpm_wait_for_suppliers() doesn't
> > > check this flag before triggering dpm_wait, leading to potential hang
> > > during suspend/resume.
> >
> > Have you seen this happen or is it just a theory?
>
> We initially see this with a downstream kernel, but I can reproduce
> this with the upstream kernel when I connect the usb host controller
> to a "usb-a-connector" node on MT8186 Corsola Chromebook. The
> devicetree looks like:
>
> usb-a-connector {
>         compatible = "usb-a-connector";
>         port {
>                 usb_a_con: endpoint {
>                         remote-endpoint = <&usb_hs>;
>                 };
>         };
> };
>
> usb_host {
>         compatible = "mediatek,mt8186-xhci", "mediatek,mtk-xhci";
>         port {
>                 usb_hs: endpoint {
>                         remote-endpoint = <&usb_a_con>;
>                 };
>         };
> };
>
> In this case, the two nodes form a cycle and I ended up seeing a
> SYNC_STATE_ONLY devlink from usb_host (supplier) to the
> usb-a-connector (consumer).

It would be good to add the above information to the patch changelog.

> I'm not very sure why we didn't see this issue before. Maybe it's
> related to the fact that the usb-a-connector has a compatible string
> (so a platform device is created) but no driver binds into it.
> >
> > > Add DL_FLAG_SYNC_STATE_ONLY in dpm_wait_for_consumers() and
> > > dpm_wait_for_suppliers() to fix this.
> >
> > The above sentence is incomplete AFAICS.
>
> Sorry, I meant "Add a check for DL_FLAG_SYNC_STATE_ONLY in ...". I'll
> update this in the next version.
> >
> > > Fixes: 05ef983e0d65a ("driver core: Add device link support for SYNC_STATE_ONLY flag")
> > > Signed-off-by: Pin-yen Lin <treapking@chromium.org>
> > > ---
> > >
> > >  drivers/base/power/main.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > > index 2ea6e05e6ec90..3271f4af2cb65 100644
> > > --- a/drivers/base/power/main.c
> > > +++ b/drivers/base/power/main.c
> > > @@ -282,7 +282,8 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
> > >          * walking.
> > >          */
> > >         list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
> > > -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> > > +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> > > +                   !device_link_test(link, DL_FLAG_SYNC_STATE_ONLY))
> >
> > This should use a check like device_link_flag_is_sync_state_only(),
> > which is different from the above one, for consistency with
> > device_reorder_to_tail().
>
> Thanks. I'll fix this in the next version.

Thanks!