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Message-ID: <20160604211014.GA29509@kroah.com>
Date: Sat, 4 Jun 2016 14:10:14 -0700
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-nvdimm@...ts.01.org, david@...morbit.com,
linux-kernel@...r.kernel.org, hch@....de
Subject: Re: [PATCH 01/13] driver core, libnvdimm: disable manual unbind of
dimms while region active
On Sat, Jun 04, 2016 at 01:52:38PM -0700, Dan Williams wrote:
> There are scenarios where we need a middle ground between disabling all
> manual bind/unbind attempts (via driver->suppress_bind_attrs) and
> allowing unbind at any userspace-determined time. Pinning modules takes
> away one vector for unwanted out-of-sequence device_release_driver()
> invocations, this new mechanism (via device->suppress_unbind_attr) takes
> away another.
>
> The first user of this mechanism is the libnvdimm sub-system where
> manual dimm disabling should be prevented while the dimm is active in
> any region. Note that there is a 1:N dimm-to-region relationship which
> is why this is implemented as a disable count rather than a flag. This
> forces userspace to disable regions before dimms when manually shutting
> down a bus topology.
>
> This does not affect any of the kernel-internal initiated invocations of
> device_release_driver().
>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
> drivers/base/base.h | 1 +
> drivers/base/bus.c | 12 ++++++++++--
> drivers/base/core.c | 1 +
> drivers/base/dd.c | 2 +-
> drivers/nvdimm/namespace_devs.c | 1 +
> drivers/nvdimm/region_devs.c | 4 +++-
> include/linux/device.h | 20 ++++++++++++++++++++
> 7 files changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index e05db388bd1c..129814b17ca6 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -109,6 +109,7 @@ extern int bus_add_driver(struct device_driver *drv);
> extern void bus_remove_driver(struct device_driver *drv);
>
> extern void driver_detach(struct device_driver *drv);
> +extern void __device_release_driver(struct device *dev);
> extern int driver_probe_device(struct device_driver *drv, struct device *dev);
> extern void driver_deferred_probe_del(struct device *dev);
> static inline int driver_match_device(struct device_driver *drv,
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 6470eb8088f4..b48a903f2d28 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -188,10 +188,18 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf,
> if (dev && dev->driver == drv) {
> if (dev->parent) /* Needed for USB */
> device_lock(dev->parent);
> - device_release_driver(dev);
> +
> + device_lock(dev);
> + if (atomic_read(&dev->suppress_unbind_attr) > 0)
> + err = -EBUSY;
> + else {
> + __device_release_driver(dev);
> + err = count;
> + }
> + device_unlock(dev);
> +
> if (dev->parent)
> device_unlock(dev->parent);
> - err = count;
> }
> put_device(dev);
> bus_put(bus);
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 0a8bdade53f2..0ea0e8560e1d 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -708,6 +708,7 @@ void device_initialize(struct device *dev)
> INIT_LIST_HEAD(&dev->devres_head);
> device_pm_init(dev);
> set_dev_node(dev, -1);
> + atomic_set(&dev->suppress_unbind_attr, 0);
> #ifdef CONFIG_GENERIC_MSI_IRQ
> INIT_LIST_HEAD(&dev->msi_list);
> #endif
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 16688f50729c..9e21817ca2d6 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -756,7 +756,7 @@ EXPORT_SYMBOL_GPL(driver_attach);
> * __device_release_driver() must be called with @dev lock held.
> * When called for a USB interface, @dev->parent lock must be held as well.
> */
> -static void __device_release_driver(struct device *dev)
> +void __device_release_driver(struct device *dev)
> {
> struct device_driver *drv;
>
> diff --git a/drivers/nvdimm/namespace_devs.c b/drivers/nvdimm/namespace_devs.c
> index c5e3196c45b0..e65572b6092c 100644
> --- a/drivers/nvdimm/namespace_devs.c
> +++ b/drivers/nvdimm/namespace_devs.c
> @@ -1950,6 +1950,7 @@ static int init_active_labels(struct nd_region *nd_region)
> }
> nd_mapping->ndd = ndd;
> atomic_inc(&nvdimm->busy);
> + device_disable_unbind_attr(&nvdimm->dev);
> get_ndd(ndd);
>
> count = nd_label_active_count(ndd);
> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> index 40fcfea26fbb..320f0f3ea367 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -427,8 +427,10 @@ static void nd_region_notify_driver_action(struct nvdimm_bus *nvdimm_bus,
> nd_mapping->labels = NULL;
> put_ndd(ndd);
> nd_mapping->ndd = NULL;
> - if (ndd)
> + if (ndd) {
> atomic_dec(&nvdimm->busy);
> + device_enable_unbind_attr(&nvdimm->dev);
> + }
> }
>
> if (is_nd_pmem(dev))
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 38f02814d53a..d9eaa85bb9cf 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -849,6 +849,7 @@ struct device {
>
> void (*release)(struct device *dev);
> struct iommu_group *iommu_group;
> + atomic_t suppress_unbind_attr; /* disable manual unbind */
>
> bool offline_disabled:1;
> bool offline:1;
> @@ -988,6 +989,25 @@ static inline void device_lock_assert(struct device *dev)
> lockdep_assert_held(&dev->mutex);
> }
>
> +static inline bool device_disable_unbind_attr(struct device *dev)
> +{
> + bool suppressed = false;
> +
> + device_lock(dev);
> + if (dev->driver) {
> + atomic_inc(&dev->suppress_unbind_attr);
> + suppressed = true;
> + }
> + device_unlock(dev);
> +
> + return suppressed;
> +}
> +
> +static inline bool device_enable_unbind_attr(struct device *dev)
> +{
> + return atomic_dec_and_test(&dev->suppress_unbind_attr);
> +}
> +
Ick, that's a mess.
Why not just prevent the unbinding from happening in your bus when you
need it?
And as you are grabbing a lock, why is this an atomic variable?
This is just making things _really_ complex for very limited gain for
what I can tell.
thanks,
greg k-h
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