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

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Message-ID: <CAGETcx9hYrnMF8JU+KV6jvxExq3jYgdg4Z_-TyjN4RUQnV8qvA@mail.gmail.com>
Date:   Tue, 19 May 2020 21:38:07 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>
Cc:     Android Kernel Team <kernel-team@...roid.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v1] driver core: Fix handling of SYNC_STATE_ONLY +
 STATELESS device links

On Tue, May 19, 2020 at 9:36 PM 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?
>
> -Saravana
>
>  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;
> +                       }
>                 }
>
>                 /*

Forgot to add stable@...r.kernel.org. Doing that now.

-Saravana