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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 9 Jul 2021 13:28:49 +0200
Message-ID: <CAJZ5v0hZCUruTc9U64Kx0EO8iky34AR+=QeNcSafQEvcGWapLw@mail.gmail.com>
Subject: Re: [PATCH V2 1/2] driver core: Add ability to delete device links of
 unregistered devices
To:     Adrian Hunter <adrian.hunter@intel.com>
Cc:     "Rafael J . Wysocki" <rafael@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Saravana Kannan <saravanak@google.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "open list:TARGET SUBSYSTEM" <linux-scsi@vger.kernel.org>,
        Avri Altman <avri.altman@wdc.com>,
        Bean Huo <huobean@gmail.com>, Can Guo <cang@codeaurora.org>,
        Asutosh Das <asutoshd@codeaurora.org>,
        Bart Van Assche <bvanassche@acm.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Precedence: bulk

On Fri, Jul 9, 2021 at 8:43 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> Managed device links are deleted by device_del(). However it is possible to
> add a device link to a consumer before device_add(), and then discover an
> error prevents the device from being used. In that case normally references
> to the device would be dropped and the device would be deleted. However the
> device link holds a reference to the device, so the device link and device
> remain indefinitely.
>
> Amend device link removal to accept removal of a link with an
> unregistered consumer device.
>
> To make that work nicely, the devlink_remove_symlinks() function must be
> amended to cope with the absence of the consumer's sysfs presence,
> otherwise sysfs_remove_link() will generate a warning.
>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Fixes: b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> ---
>  drivers/base/core.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index ea5b85354526..24bacdb315c6 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -562,7 +562,8 @@ static void devlink_remove_symlinks(struct device *dev,
>         struct device *con = link->consumer;
>         char *buf;
>
> -       sysfs_remove_link(&link->link_dev.kobj, "consumer");
> +       if (device_is_registered(con))
> +               sysfs_remove_link(&link->link_dev.kobj, "consumer");

I think that this is needed regardless of the changes in
device_link_put_kref(), because if somebody decides to delete a
stateless device link before registering the consumer device,
sysfs_remove_link() will still complain, won't it?

>         sysfs_remove_link(&link->link_dev.kobj, "supplier");
>
>         len = max(strlen(dev_bus_name(sup)) + strlen(dev_name(sup)),
> @@ -575,8 +576,10 @@ static void devlink_remove_symlinks(struct device *dev,
>                 return;
>         }
>
> -       snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
> -       sysfs_remove_link(&con->kobj, buf);
> +       if (device_is_registered(con)) {
> +               snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
> +               sysfs_remove_link(&con->kobj, buf);
> +       }

And here too, if I'm not mistaken.

So in that case it would be better to put the above changes into a
separate patch and add a Fixes tag to it.

>         snprintf(buf, len, "consumer:%s:%s", dev_bus_name(con), dev_name(con));
>         sysfs_remove_link(&sup->kobj, buf);
>         kfree(buf);
> @@ -885,6 +888,8 @@ static void device_link_put_kref(struct device_link *link)
>  {
>         if (link->flags & DL_FLAG_STATELESS)
>                 kref_put(&link->kref, __device_link_del);
> +       else if (!device_is_registered(link->consumer))
> +               __device_link_del(&link->kref);
>         else
>                 WARN(1, "Unable to drop a managed device link reference\n");
>  }
> --
> 2.17.1
>