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Date: Wed, 19 Dec 2018 15:27:48 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: alexander.h.duyck@...ux.intel.com
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Luis R. Rodriguez" <mcgrof@...nel.org>,
"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
Tejun Heo <tj@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux PM <linux-pm@...r.kernel.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
zwisler@...nel.org, Dan Williams <dan.j.williams@...el.com>,
dave.jiang@...el.com, bvanassche@....org
Subject: Re: [driver-core PATCH v9 1/9] driver core: Establish order of
operations for device_add and device_del via bitflag
On Thu, Dec 13, 2018 at 1:45 AM Alexander Duyck
<alexander.h.duyck@...ux.intel.com> 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.
>
> One additional change added was that I pulled the check for dev->driver
> out of the __device_attach_driver call and instead placed it in the
> __device_attach_async_helper call. This was motivated by the fact that the
> only other caller of this, __device_attach, had already taken the
> device_lock() and checked for dev->driver. Instead of testing for this
> twice in this path it makes more sense to just consolidate the dev->dead
> and dev->driver checks together into one set of checks.
>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> drivers/base/core.c | 11 +++++++++++
> drivers/base/dd.c | 22 +++++++++++-----------
> include/linux/device.h | 5 +++++
> 3 files changed, 27 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 0073b09bb99f..950e25495726 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2080,6 +2080,17 @@ 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..74c194ac99df 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -731,15 +731,6 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
> bool async_allowed;
> int ret;
>
> - /*
> - * Check if device has already been claimed. This may
> - * happen with driver loading, device discovery/registration,
> - * and deferred probe processing happens all at once with
> - * multiple threads.
> - */
> - if (dev->driver)
> - return -EBUSY;
> -
> ret = driver_match_device(drv, dev);
> if (ret == 0) {
> /* no match */
> @@ -774,6 +765,15 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
>
> device_lock(dev);
>
> + /*
> + * Check if device has already been removed or claimed. This may
> + * happen with driver loading, device discovery/registration,
> + * and deferred probe processing happens all at once with
> + * multiple threads.
> + */
> + if (dev->dead || dev->driver)
> + goto out_unlock;
> +
> if (dev->parent)
> pm_runtime_get_sync(dev->parent);
>
> @@ -784,7 +784,7 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
>
> if (dev->parent)
> pm_runtime_put(dev->parent);
> -
> +out_unlock:
> device_unlock(dev);
>
> put_device(dev);
> @@ -897,7 +897,7 @@ static int __driver_attach(struct device *dev, void *data)
> if (dev->parent && dev->bus->need_parent_lock)
> device_lock(dev->parent);
> device_lock(dev);
> - if (!dev->driver)
> + if (!dev->dead && !dev->driver)
> driver_probe_device(drv, dev);
> device_unlock(dev);
> if (dev->parent && dev->bus->need_parent_lock)
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 1b25c7a43f4c..f73dad81e811 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -957,6 +957,10 @@ struct dev_links_info {
> * device.
> * @dma_coherent: this particular device is dma coherent, even if the
> * architecture supports non-coherent devices.
> + * @dead: This device is currently either in the process of or has
> + * been removed from the system. Any asynchronous events
> + * scheduled for this device should exit without taking any
> + * action.
> *
> * 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 +1055,7 @@ struct device {
> defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
> bool dma_coherent:1;
> #endif
> + bool dead:1;
> };
>
> static inline struct device *kobj_to_dev(struct kobject *kobj)
>
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