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Date: Thu, 31 May 2018 08:31:18 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Alan Stern <stern@...land.harvard.edu>
Cc: Martin Liu <liumartin@...gle.com>, heikki.krogerus@...ux.intel.com,
johan@...nel.org, andy.shevchenko@...il.com,
linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
jenhaochen@...gle.com
Subject: Re: [PATCH v4] driver core: hold dev's parent lock when needed
On Wed, May 30, 2018 at 01:21:02PM -0400, Alan Stern wrote:
> On Thu, 31 May 2018, Martin Liu wrote:
>
> > SoC have internal I/O buses that can't be proved for devices. The
> > devices on the buses can be accessed directly without additinal
> > configuration required. This type of bus is represented as
> > "simple-bus". In some platforms, we name "soc" with "simple-bus"
> > attribute and many devices are hooked under it described in DT
> > (device tree).
> >
> > In commit bf74ad5bc417 ("Hold the device's parent's lock during
> > probe and remove") to solve USB subsystem lock sequence since
> > USB device's characteristic. Thus "soc" needs to be locked
> > whenever a device and driver's probing happen under "soc" bus.
> > During this period, an async driver tries to probe a device which
> > is under the "soc" bus would be blocked until previous driver
> > finish the probing and release "soc" lock. And the next probing
> > under the "soc" bus need to wait for async finish. Because of
> > that, driver's async probe for init time improvement will be
> > shadowed.
> >
> > Since many devices don't have USB devices' characteristic, they
> > actually don't need parent's lock. Thus, we introduce a lock flag
> > in bus_type struct and driver core would lock the parent lock base
> > on the flag. For USB, we set this flag in usb_bus_type to keep
> > original lock behavior in driver core.
> >
> > Async probe could have more benefit after this patch.
> >
> > Signed-off-by: Martin Liu <liumartin@...gle.com>
> > ---
> > Changes in v4:
> > -fix comment and wording.
> > -follow the suggestion.
> >
> > [v3]: https://lkml.org/lkml/2018/5/29/876
> > [v2]: https://lkml.org/lkml/2018/5/29/108
> > [v1]: https://lkml.org/lkml/2018/5/22/545
> >
> > drivers/base/bus.c | 16 ++++++++--------
> > drivers/base/dd.c | 8 ++++----
> > drivers/usb/core/driver.c | 1 +
> > include/linux/device.h | 3 +++
> > 4 files changed, 16 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> > index ef6183306b40..8bfd27ec73d6 100644
> > --- a/drivers/base/bus.c
> > +++ b/drivers/base/bus.c
> > @@ -184,10 +184,10 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf,
> >
> > dev = bus_find_device_by_name(bus, NULL, buf);
> > if (dev && dev->driver == drv) {
> > - if (dev->parent) /* Needed for USB */
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_lock(dev->parent);
> > device_release_driver(dev);
> > - if (dev->parent)
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_unlock(dev->parent);
> > err = count;
> > }
> > @@ -211,12 +211,12 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf,
> >
> > dev = bus_find_device_by_name(bus, NULL, buf);
> > if (dev && dev->driver == NULL && driver_match_device(drv, dev)) {
> > - if (dev->parent) /* Needed for USB */
> > + if (dev->parent && bus->need_parent_lock)
> > device_lock(dev->parent);
> > device_lock(dev);
> > err = driver_probe_device(drv, dev);
> > device_unlock(dev);
> > - if (dev->parent)
> > + if (dev->parent && bus->need_parent_lock)
> > device_unlock(dev->parent);
> >
> > if (err > 0) {
> > @@ -735,10 +735,10 @@ static int __must_check bus_rescan_devices_helper(struct device *dev,
> > int ret = 0;
> >
> > if (!dev->driver) {
> > - if (dev->parent) /* Needed for USB */
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_lock(dev->parent);
> > ret = device_attach(dev);
> > - if (dev->parent)
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_unlock(dev->parent);
> > }
> > return ret < 0 ? ret : 0;
> > @@ -770,10 +770,10 @@ EXPORT_SYMBOL_GPL(bus_rescan_devices);
> > int device_reprobe(struct device *dev)
> > {
> > if (dev->driver) {
> > - if (dev->parent) /* Needed for USB */
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_lock(dev->parent);
> > device_release_driver(dev);
> > - if (dev->parent)
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_unlock(dev->parent);
> > }
> > return bus_rescan_devices_helper(dev, NULL);
> > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > index c9f54089429b..7c09f73b96f3 100644
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -817,13 +817,13 @@ static int __driver_attach(struct device *dev, void *data)
> > return ret;
> > } /* ret > 0 means positive match */
> >
> > - if (dev->parent) /* Needed for USB */
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_lock(dev->parent);
> > device_lock(dev);
> > if (!dev->driver)
> > driver_probe_device(drv, dev);
> > device_unlock(dev);
> > - if (dev->parent)
> > + if (dev->parent && dev->bus->need_parent_lock)
> > device_unlock(dev->parent);
> >
> > return 0;
> > @@ -919,7 +919,7 @@ void device_release_driver_internal(struct device *dev,
> > struct device_driver *drv,
> > struct device *parent)
> > {
> > - if (parent)
> > + if (parent && dev->bus->need_parent_lock)
> > device_lock(parent);
> >
> > device_lock(dev);
> > @@ -927,7 +927,7 @@ void device_release_driver_internal(struct device *dev,
> > __device_release_driver(dev, parent);
> >
> > device_unlock(dev);
> > - if (parent)
> > + if (parent && dev->bus->need_parent_lock)
> > device_unlock(parent);
> > }
> >
> > diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> > index 9792cedfc351..e76e95f62f76 100644
> > --- a/drivers/usb/core/driver.c
> > +++ b/drivers/usb/core/driver.c
> > @@ -1922,4 +1922,5 @@ struct bus_type usb_bus_type = {
> > .name = "usb",
> > .match = usb_device_match,
> > .uevent = usb_uevent,
> > + .need_parent_lock = true,
> > };
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 477956990f5e..beca424395dd 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -98,6 +98,8 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *);
> > * @lock_key: Lock class key for use by the lock validator
> > * @force_dma: Assume devices on this bus should be set up by dma_configure()
> > * even if DMA capability is not explicitly described by firmware.
> > + * @need_parent_lock: When probing or removing a device on this bus, the
> > + * device core should lock the device's parent.
> > *
> > * A bus is a channel between the processor and one or more devices. For the
> > * purposes of the device model, all devices are connected via a bus, even if
> > @@ -138,6 +140,7 @@ struct bus_type {
> > struct lock_class_key lock_key;
> >
> > bool force_dma;
> > + bool need_parent_lock;
> > };
> >
> > extern int __must_check bus_register(struct bus_type *bus);
>
> This looks okay to me.
>
> Acked-by: Alan Stern <stern@...land.harvard.edu>
>
> Greg, any more comments?
Looks sane to me. Martin, thanks for all of the changes.
greg k-h
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