Re: [driver-core PATCH v8 2/9] driver core: Establish order of operations for device_add and device_del via bitflag

[Dan Williams]

On Wed, Dec 5, 2018 at 9:25 AM Alexander Duyck
<alexander.h.duyck@xxxxxxxxxxxxxxx> wrote:
>
> Add an additional bit flag to the device struct named "dead".
>
> This additional flag provides a guarantee that when a device_del is
> executed on a given interface an async worker will not attempt to attach
> the driver following the earlier device_del call. Previously this
> guarantee was not present and could result in the device_del call
> attempting to remove a driver from an interface only to have the async
> worker attempt to probe the driver later when it finally completes the
> asynchronous probe call.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> ---
>  drivers/base/core.c    |   11 +++++++++++
>  drivers/base/dd.c      |    8 ++++++--
>  include/linux/device.h |    5 +++++
>  3 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f3e6ca4170b4..70358327303b 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2075,6 +2075,17 @@ void device_del(struct device *dev)
>         struct kobject *glue_dir = NULL;
>         struct class_interface *class_intf;
>
> +       /*
> +        * Hold the device lock and set the "dead" flag to guarantee that
> +        * the update behavior is consistent with the other bitfields near
> +        * it and that we cannot have an asynchronous probe routine trying
> +        * to run while we are tearing out the bus/class/sysfs from
> +        * underneath the device.
> +        */
> +       device_lock(dev);
> +       dev->dead = true;
> +       device_unlock(dev);
> +
>         /* Notify clients of device removal.  This call must come
>          * before dpm_sysfs_remove().
>          */
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 88713f182086..3bb8c3e0f3da 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -774,6 +774,10 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
>
>         device_lock(dev);
>
> +       /* device is or has been removed from the bus, just bail out */
> +       if (dev->dead)
> +               goto out_unlock;
> +

What do you think about moving this check into
__device_attach_driver() alongside all the other checks? That way we
also get ->dead checking through the __device_attach() path.

...and after that maybe it could be made a common helper
(dev_driver_checks()?) shared between __device_attach_driver() and
__driver_attach() to reduce some duplication.