linux-kernel - Re: [PATCH] PM: sleep: Don't wait for SYNC_STATE

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Message-ID: <CAJZ5v0jNytfP8W2XSyBNLe8OsD=O9M7WWvhtxdwXA-5KxwKfbg@mail.gmail.com>
Date: Wed, 10 Sep 2025 13:56:44 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Pin-yen Lin <treapking@...omium.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, Pavel Machek <pavel@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, Hsin-Te Yuan <yuanhsinte@...omium.org>, 
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	Chen-Yu Tsai <wenst@...omium.org>
Subject: Re: [PATCH] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

On Tue, Sep 9, 2025 at 11:44 AM Pin-yen Lin <treapking@...omium.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@...omium.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);
> --