linux-kernel - Re: [PATCH v1] driver core: Fix handling of SYNC_STATE

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Date:   Wed, 20 May 2020 11:13:03 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] driver core: Fix handling of SYNC_STATE_ONLY +
 STATELESS device links

On Wed, May 20, 2020 at 6:36 AM Saravana Kannan <saravanak@...gle.com> wrote:
>
> Commit 21c27f06587d ("driver core: Fix SYNC_STATE_ONLY device link
> implementation") didn't completely fix STATELESS + SYNC_STATE_ONLY
> handling.
>
> What looks like an optimization in that commit is actually a bug that
> causes an if condition to always take the else path. This prevents
> reordering of devices in the dpm_list when a DL_FLAG_STATELESS device
> link is create on top of an existing DL_FLAG_SYNC_STATE_ONLY device
> link.
>
> Fixes: 21c27f06587d ("driver core: Fix SYNC_STATE_ONLY device link implementation")
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> ---
> Sigh... device links are tricky and hard! Sorry about the endless fixes :(
> Also, how was this not caught by the compiler as a warning?

Well, I haven't spotted this either ...

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

>  drivers/base/core.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 83a3e0b62ce3..dfd4e94ef790 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -543,12 +543,14 @@ struct device_link *device_link_add(struct device *consumer,
>
>                 if (flags & DL_FLAG_STATELESS) {
>                         kref_get(&link->kref);
> -                       link->flags |= DL_FLAG_STATELESS;
>                         if (link->flags & DL_FLAG_SYNC_STATE_ONLY &&
> -                           !(link->flags & DL_FLAG_STATELESS))
> +                           !(link->flags & DL_FLAG_STATELESS)) {
> +                               link->flags |= DL_FLAG_STATELESS;
>                                 goto reorder;
> -                       else
> +                       } else {
> +                               link->flags |= DL_FLAG_STATELESS;
>                                 goto out;
> +                       }
>                 }
>
>                 /*
> --
> 2.26.2.761.g0e0b3e54be-goog
>