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SubjectRe: [PATCH] driver core: fix shutdown races with probe/remove(v1)
On Fri, 8 Jun 2012, Ming Lei wrote:

> Firstly, .shutdown callback may touch a uninitialized hardware
> if dev->driver is set and .probe is not completed.
>
> Secondly, device_shutdown() may dereference a null pointer to cause
> oops when dev->driver is cleared after it is checked in
> device_shutdown().
>
> So just hold device lock and its parent lock if it has to fix the
> races.
>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
> drivers/base/core.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 346be8b..cbc8bd2 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1820,6 +1820,11 @@ void device_shutdown(void)
> list_del_init(&dev->kobj.entry);
> spin_unlock(&devices_kset->list_lock);
>
> + /*hold lock[s] to avoid races with .probe/.release*/
> + if (dev->parent)
> + device_lock(dev->parent);
> + device_lock(dev);

Would you prefer to use device_trylock in a loop? I guess this comes
down to which you prefer: a hang during shutdown, or a crash. :-)

Alan Stern



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