Re: [PATCH v3] driver core: Update device link status correctly for SYNC_STATE_ONLY links

["Rafael J. Wysocki" <rafael@kernel.org>]

On Wed, May 27, 2020 at 12:09 AM Saravana Kannan <saravanak@google.com> wrote:
>
> When SYNC_STATE_ONLY support was added in commit 05ef983e0d65 ("driver
> core: Add device link support for SYNC_STATE_ONLY flag"),
> SYNC_STATE_ONLY links were treated similar to STATELESS links in terms
> of not blocking consumer probe if the supplier hasn't probed yet.
>
> That caused a SYNC_STATE_ONLY device link's status to not get updated.
> Since SYNC_STATE_ONLY device link is no longer useful once the
> consumer probes, commit 21c27f06587d ("driver core: Fix
> SYNC_STATE_ONLY device link implementation") addresses the status
> update issue by deleting the SYNC_STATE_ONLY device link instead of
> complicating the status update code.
>
> However, there are still some cases where we need to update the status
> of a SYNC_STATE_ONLY device link. This is because a SYNC_STATE_ONLY
> device link can later get converted into a normal MANAGED device link
> when a normal MANAGED device link is created between a supplier and
> consumer that already have a SYNC_STATE_ONLY device link between them.
>
> If a SYNC_STATE_ONLY device link's status isn't maintained correctly
> till it's converted to a normal MANAGED device link, then the normal
> MANAGED device link will end up with a wrong link status. This can cause
> a warning stack trace[1] when the consumer device probes successfully.
>
> This commit fixes the SYNC_STATE_ONLY device link status update issue
> where it wouldn't transition correctly from DL_STATE_DORMANT or
> DL_STATE_AVAILABLE to DL_STATE_CONSUMER_PROBE. It also resets the status
> back to DL_STATE_DORMANT or DL_STATE_AVAILABLE if the consumer probe
> fails.
>
> [1] - https://lore.kernel.org/lkml/20200522204120.3b3c9ed6@apollo/
> Fixes: 05ef983e0d65 ("driver core: Add device link support for SYNC_STATE_ONLY flag")
> Fixes: 21c27f06587d ("driver core: Fix SYNC_STATE_ONLY device link implementation")
> Reported-by: Michael Walle <michael@walle.cc>
> Tested-by: Michael Walle <michael@walle.cc>
> Signed-off-by: Saravana Kannan <saravanak@google.com>

Reviewed-by: Rafael J. Wysocki <rrafael.j.wysocki@intel.com>

> ---
> v1->v2:
> - Added code to "revert" the link status if consumer probe fails
>
> v2->v3:
> - Fixed copy-pasta where I was checking link->status instead of
>   link->flags.
>
>  drivers/base/core.c | 34 ++++++++++++++++++++++++++--------
>  1 file changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 791b7530599f..9a76dd44cb37 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -646,9 +646,17 @@ static void device_links_missing_supplier(struct device *dev)
>  {
>         struct device_link *link;
>
> -       list_for_each_entry(link, &dev->links.suppliers, c_node)
> -               if (link->status == DL_STATE_CONSUMER_PROBE)
> +       list_for_each_entry(link, &dev->links.suppliers, c_node) {
> +               if (link->status != DL_STATE_CONSUMER_PROBE)
> +                       continue;
> +
> +               if (link->supplier->links.status == DL_DEV_DRIVER_BOUND) {
>                         WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
> +               } else {
> +                       WARN_ON(!(link->flags & DL_FLAG_SYNC_STATE_ONLY));
> +                       WRITE_ONCE(link->status, DL_STATE_DORMANT);
> +               }
> +       }
>  }
>
>  /**
> @@ -687,11 +695,11 @@ int device_links_check_suppliers(struct device *dev)
>         device_links_write_lock();
>
>         list_for_each_entry(link, &dev->links.suppliers, c_node) {
> -               if (!(link->flags & DL_FLAG_MANAGED) ||
> -                   link->flags & DL_FLAG_SYNC_STATE_ONLY)
> +               if (!(link->flags & DL_FLAG_MANAGED))
>                         continue;
>
> -               if (link->status != DL_STATE_AVAILABLE) {
> +               if (link->status != DL_STATE_AVAILABLE &&
> +                   !(link->flags & DL_FLAG_SYNC_STATE_ONLY)) {
>                         device_links_missing_supplier(dev);
>                         ret = -EPROBE_DEFER;
>                         break;
> @@ -952,11 +960,21 @@ static void __device_links_no_driver(struct device *dev)
>                 if (!(link->flags & DL_FLAG_MANAGED))
>                         continue;
>
> -               if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER)
> +               if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER) {
>                         device_link_drop_managed(link);
> -               else if (link->status == DL_STATE_CONSUMER_PROBE ||
> -                        link->status == DL_STATE_ACTIVE)
> +                       continue;
> +               }
> +
> +               if (link->status != DL_STATE_CONSUMER_PROBE &&
> +                   link->status != DL_STATE_ACTIVE)
> +                       continue;
> +
> +               if (link->supplier->links.status == DL_DEV_DRIVER_BOUND) {
>                         WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
> +               } else {
> +                       WARN_ON(!(link->flags & DL_FLAG_SYNC_STATE_ONLY));
> +                       WRITE_ONCE(link->status, DL_STATE_DORMANT);
> +               }
>         }
>
>         dev->links.status = DL_DEV_NO_DRIVER;
> --
> 2.27.0.rc0.183.gde8f92d652-goog
>