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Message-ID: <20181130234038.GF28501@garbanzo.do-not-panic.com>
Date: Fri, 30 Nov 2018 15:40:38 -0800
From: Luis Chamberlain <mcgrof@...nel.org>
To: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
linux-nvdimm@...ts.01.org, tj@...nel.org,
akpm@...ux-foundation.org, linux-pm@...r.kernel.org,
jiangshanlai@...il.com, rafael@...nel.org, len.brown@...el.com,
pavel@....cz, zwisler@...nel.org, dan.j.williams@...el.com,
dave.jiang@...el.com, bvanassche@....org,
dmitry.torokhov@...il.com, brendanhiggins@...gle.com
Subject: Re: [driver-core PATCH v7 2/9] driver core: Establish clear order of
operations for deferred probe and remove
On Wed, Nov 28, 2018 at 04:32:16PM -0800, Alexander Duyck wrote:
> Add an additional bit flag to the device struct named async_probe. This
> additional flag allows us to guarantee ordering between probe and remove
> operations.
>
> This allows us to guarantee that if we execute a remove operation on a
> given interface it will not attempt to update the driver member
> asynchronously following the earlier operation. Previously this guarantee
> was not present and could result in us attempting to remove a driver from
> an interface only to have it attempt to attach the driver later when we
> finally complete the deferred asynchronous probe call.
>
> Reviewed-by: Bart Van Assche <bvanassche@....org>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
This is the sort of corner case that is best if we had a test case for
it, as it is hard to reproduce and -- how do we know we won't regress
later? Not sure if it helps but we have lib/test_kmod.c and its
respective tools/testing/selftests/kmod/kmod.sh, a new enum kmod_test_case
might be in order for device emulation creeping up / disappearing
during a custom mock driver using async probe.
Yeah.. I know.. "yes this seems good but how about later"? While we're going
through the motions here and have your attention on this I think it
would be valuable for this now. This is the sort of code that won't
change often, but if modified *can* really break things badly.
Luis
> ---
> drivers/base/dd.c | 16 ++++++++++++++++
> include/linux/device.h | 3 +++
> 2 files changed, 19 insertions(+)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 88713f182086..ef3f70a7cb5a 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);
>
> + /* nothing to do if async_probe has been cleared */
> + if (!dev->async_probe)
> + goto out_unlock;
> +
> if (dev->parent)
> pm_runtime_get_sync(dev->parent);
>
> @@ -785,6 +789,9 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
> if (dev->parent)
> pm_runtime_put(dev->parent);
>
> + /* We made our attempt at an async_probe, clear the flag */
> + dev->async_probe = false;
> +out_unlock:
> device_unlock(dev);
>
> put_device(dev);
> @@ -829,6 +836,7 @@ static int __device_attach(struct device *dev, bool allow_async)
> */
> dev_dbg(dev, "scheduling asynchronous probe\n");
> get_device(dev);
> + dev->async_probe = true;
> async_schedule(__device_attach_async_helper, dev);
> } else {
> pm_request_idle(dev);
> @@ -929,6 +937,14 @@ static void __device_release_driver(struct device *dev, struct device *parent)
> {
> struct device_driver *drv;
>
> + /*
> + * In the event that we are asked to release the driver on an
> + * interface that is still waiting on a probe we can just terminate
> + * the probe by setting async_probe to false. When the async call
> + * is finally completed it will see this state and just exit.
> + */
> + dev->async_probe = false;
> +
> drv = dev->driver;
> if (drv) {
> while (device_links_busy(dev)) {
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 1b25c7a43f4c..4d2eb2c74149 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -957,6 +957,8 @@ struct dev_links_info {
> * device.
> * @dma_coherent: this particular device is dma coherent, even if the
> * architecture supports non-coherent devices.
> + * @async_probe: This device has an asynchronous probe event pending. Should
> + * only be updated while holding device lock.
> *
> * At the lowest level, every device in a Linux system is represented by an
> * instance of struct device. The device structure contains the information
> @@ -1051,6 +1053,7 @@ struct device {
> defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
> bool dma_coherent:1;
> #endif
> + bool async_probe:1;
> };
>
> static inline struct device *kobj_to_dev(struct kobject *kobj)
>
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