3:18 a.m.
On Mon, 2018-11-05 at 17:04 -0800, Bart Van Assche wrote:
On Mon, 2018-11-05 at 13:11 -0800, Alexander Duyck wrote:
> This patch moves the async_synchronize_full call out of
> __device_release_driver and into driver_detach.
>
> The idea behind this is that the async_synchronize_full call will only
> guarantee that any existing async operations are flushed. This doesn't do
> anything to guarantee that a hotplug event that may occur while we are
> doing the release of the driver will not be asynchronously scheduled.
>
> By moving this into the driver_detach path we can avoid potential deadlocks
> as we aren't holding the device lock at this point and we should not have
> the driver we want to flush loaded so the flush will take care of any
> asynchronous events the driver we are detaching might have scheduled.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck(a)linux.intel.com>
> ---
> drivers/base/dd.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 76c40fe69463..e74cefeb5b69 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -975,9 +975,6 @@ static void __device_release_driver(struct device *dev, struct
device *parent)
>
> drv = dev->driver;
> if (drv) {
> - if (driver_allows_async_probing(drv))
> - async_synchronize_full();
> -
> while (device_links_busy(dev)) {
> __device_driver_unlock(dev, parent);
>
> @@ -1087,6 +1084,9 @@ void driver_detach(struct device_driver *drv)
> struct device_private *dev_prv;
> struct device *dev;
>
> + if (driver_allows_async_probing(drv))
> + async_synchronize_full();
> +
> for (;;) {
> spin_lock(&drv->p->klist_devices.k_lock);
> if (list_empty(&drv->p->klist_devices.k_list)) {
Have you considered to move that async_synchronize_full() call into
bus_remove_driver()? Verifying the correctness of this patch requires to
check whether the async_synchronize_full() comes after the
klist_remove(&drv->p->knode_bus) call. That verification is easier when
the async_synchronize_full() call occurs in bus_remove_driver() instead
of in driver_detach().
Thanks,
Bart.
I considered it, however it ends up with things being more symmetric to
have use take care of synchronizing things in driver_detach since after
this patch set we are scheduling thing asynchronously in driver_attach.
Also I don't think it would be any great risk simply because calling
driver_detach with the driver still associated with the bus would be a
blatent error as it could easily lead to issues where you unbind a
driver but have it get hotplugged to a device while that is going on.
- Alex