| Message ID | 1522219661-26827-2-git-send-email-andr2000@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Mar 28, 2018 at 09:47:40AM +0300, Oleksandr Andrushchenko wrote: > From: Noralf Trønnes <noralf@tronnes.org> > > Use srcu to protect drm_device.unplugged in a race free manner. > Drivers can use drm_dev_enter()/drm_dev_exit() to protect and mark > sections preventing access to device resources that are not available > after the device is gone. > > Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch> > Signed-off-by: Noralf Trønnes <noralf@tronnes.org> > Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com> > Tested-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com> > Cc: intel-gfx@lists.freedesktop.org When you apply/forward a patch we also need your s-o-b line, even if you changed nothing. sob needs to reflect the full record of everyone who handled a patch from author to when it finally lands in git. -Daniel > --- > drivers/gpu/drm/drm_drv.c | 54 ++++++++++++++++++++++++++++++++++++++++++----- > include/drm/drm_device.h | 9 +++++++- > include/drm/drm_drv.h | 15 +++++++++---- > 3 files changed, 68 insertions(+), 10 deletions(-) > > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c > index a1b9338736e3..32a83b41ab61 100644 > --- a/drivers/gpu/drm/drm_drv.c > +++ b/drivers/gpu/drm/drm_drv.c > @@ -32,6 +32,7 @@ > #include <linux/moduleparam.h> > #include <linux/mount.h> > #include <linux/slab.h> > +#include <linux/srcu.h> > > #include <drm/drm_drv.h> > #include <drm/drmP.h> > @@ -75,6 +76,8 @@ static bool drm_core_init_complete = false; > > static struct dentry *drm_debugfs_root; > > +DEFINE_STATIC_SRCU(drm_unplug_srcu); > + > /* > * DRM Minors > * A DRM device can provide several char-dev interfaces on the DRM-Major. Each > @@ -318,18 +321,51 @@ void drm_put_dev(struct drm_device *dev) > } > EXPORT_SYMBOL(drm_put_dev); > > -static void drm_device_set_unplugged(struct drm_device *dev) > +/** > + * drm_dev_enter - Enter device critical section > + * @dev: DRM device > + * @idx: Pointer to index that will be passed to the matching drm_dev_exit() > + * > + * This function marks and protects the beginning of a section that should not > + * be entered after the device has been unplugged. The section end is marked > + * with drm_dev_exit(). Calls to this function can be nested. > + * > + * Returns: > + * True if it is OK to enter the section, false otherwise. > + */ > +bool drm_dev_enter(struct drm_device *dev, int *idx) > +{ > + *idx = srcu_read_lock(&drm_unplug_srcu); > + > + if (dev->unplugged) { > + srcu_read_unlock(&drm_unplug_srcu, *idx); > + return false; > + } > + > + return true; > +} > +EXPORT_SYMBOL(drm_dev_enter); > + > +/** > + * drm_dev_exit - Exit device critical section > + * @idx: index returned from drm_dev_enter() > + * > + * This function marks the end of a section that should not be entered after > + * the device has been unplugged. > + */ > +void drm_dev_exit(int idx) > { > - smp_wmb(); > - atomic_set(&dev->unplugged, 1); > + srcu_read_unlock(&drm_unplug_srcu, idx); > } > +EXPORT_SYMBOL(drm_dev_exit); > > /** > * drm_dev_unplug - unplug a DRM device > * @dev: DRM device > * > * This unplugs a hotpluggable DRM device, which makes it inaccessible to > - * userspace operations. Entry-points can use drm_dev_is_unplugged(). This > + * userspace operations. Entry-points can use drm_dev_enter() and > + * drm_dev_exit() to protect device resources in a race free manner. This > * essentially unregisters the device like drm_dev_unregister(), but can be > * called while there are still open users of @dev. > */ > @@ -338,10 +374,18 @@ void drm_dev_unplug(struct drm_device *dev) > drm_dev_unregister(dev); > > mutex_lock(&drm_global_mutex); > - drm_device_set_unplugged(dev); > if (dev->open_count == 0) > drm_dev_put(dev); > mutex_unlock(&drm_global_mutex); > + > + /* > + * After synchronizing any critical read section is guaranteed to see > + * the new value of ->unplugged, and any critical section which might > + * still have seen the old value of ->unplugged is guaranteed to have > + * finished. > + */ > + dev->unplugged = true; > + synchronize_srcu(&drm_unplug_srcu); > } > EXPORT_SYMBOL(drm_dev_unplug); > > diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h > index 7c4fa32f3fc6..3a0eac2885b7 100644 > --- a/include/drm/drm_device.h > +++ b/include/drm/drm_device.h > @@ -46,7 +46,14 @@ struct drm_device { > /* currently active master for this device. Protected by master_mutex */ > struct drm_master *master; > > - atomic_t unplugged; /**< Flag whether dev is dead */ > + /** > + * @unplugged: > + * > + * Flag to tell if the device has been unplugged. > + * See drm_dev_enter() and drm_dev_is_unplugged(). > + */ > + bool unplugged; > + > struct inode *anon_inode; /**< inode for private address-space */ > char *unique; /**< unique name of the device */ > /*@} */ > diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h > index d23dcdd1bd95..7e545f5f94d3 100644 > --- a/include/drm/drm_drv.h > +++ b/include/drm/drm_drv.h > @@ -624,6 +624,8 @@ void drm_dev_get(struct drm_device *dev); > void drm_dev_put(struct drm_device *dev); > void drm_dev_unref(struct drm_device *dev); > void drm_put_dev(struct drm_device *dev); > +bool drm_dev_enter(struct drm_device *dev, int *idx); > +void drm_dev_exit(int idx); > void drm_dev_unplug(struct drm_device *dev); > > /** > @@ -635,11 +637,16 @@ void drm_dev_unplug(struct drm_device *dev); > * unplugged, these two functions guarantee that any store before calling > * drm_dev_unplug() is visible to callers of this function after it completes > */ > -static inline int drm_dev_is_unplugged(struct drm_device *dev) > +static inline bool drm_dev_is_unplugged(struct drm_device *dev) > { > - int ret = atomic_read(&dev->unplugged); > - smp_rmb(); > - return ret; > + int idx; > + > + if (drm_dev_enter(dev, &idx)) { > + drm_dev_exit(idx); > + return false; > + } > + > + return true; > } > > > -- > 2.7.4 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index a1b9338736e3..32a83b41ab61 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -32,6 +32,7 @@ #include <linux/moduleparam.h> #include <linux/mount.h> #include <linux/slab.h> +#include <linux/srcu.h> #include <drm/drm_drv.h> #include <drm/drmP.h> @@ -75,6 +76,8 @@ static bool drm_core_init_complete = false; static struct dentry *drm_debugfs_root; +DEFINE_STATIC_SRCU(drm_unplug_srcu); + /* * DRM Minors * A DRM device can provide several char-dev interfaces on the DRM-Major. Each @@ -318,18 +321,51 @@ void drm_put_dev(struct drm_device *dev) } EXPORT_SYMBOL(drm_put_dev); -static void drm_device_set_unplugged(struct drm_device *dev) +/** + * drm_dev_enter - Enter device critical section + * @dev: DRM device + * @idx: Pointer to index that will be passed to the matching drm_dev_exit() + * + * This function marks and protects the beginning of a section that should not + * be entered after the device has been unplugged. The section end is marked + * with drm_dev_exit(). Calls to this function can be nested. + * + * Returns: + * True if it is OK to enter the section, false otherwise. + */ +bool drm_dev_enter(struct drm_device *dev, int *idx) +{ + *idx = srcu_read_lock(&drm_unplug_srcu); + + if (dev->unplugged) { + srcu_read_unlock(&drm_unplug_srcu, *idx); + return false; + } + + return true; +} +EXPORT_SYMBOL(drm_dev_enter); + +/** + * drm_dev_exit - Exit device critical section + * @idx: index returned from drm_dev_enter() + * + * This function marks the end of a section that should not be entered after + * the device has been unplugged. + */ +void drm_dev_exit(int idx) { - smp_wmb(); - atomic_set(&dev->unplugged, 1); + srcu_read_unlock(&drm_unplug_srcu, idx); } +EXPORT_SYMBOL(drm_dev_exit); /** * drm_dev_unplug - unplug a DRM device * @dev: DRM device * * This unplugs a hotpluggable DRM device, which makes it inaccessible to - * userspace operations. Entry-points can use drm_dev_is_unplugged(). This + * userspace operations. Entry-points can use drm_dev_enter() and + * drm_dev_exit() to protect device resources in a race free manner. This * essentially unregisters the device like drm_dev_unregister(), but can be * called while there are still open users of @dev. */ @@ -338,10 +374,18 @@ void drm_dev_unplug(struct drm_device *dev) drm_dev_unregister(dev); mutex_lock(&drm_global_mutex); - drm_device_set_unplugged(dev); if (dev->open_count == 0) drm_dev_put(dev); mutex_unlock(&drm_global_mutex); + + /* + * After synchronizing any critical read section is guaranteed to see + * the new value of ->unplugged, and any critical section which might + * still have seen the old value of ->unplugged is guaranteed to have + * finished. + */ + dev->unplugged = true; + synchronize_srcu(&drm_unplug_srcu); } EXPORT_SYMBOL(drm_dev_unplug); diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h index 7c4fa32f3fc6..3a0eac2885b7 100644 --- a/include/drm/drm_device.h +++ b/include/drm/drm_device.h @@ -46,7 +46,14 @@ struct drm_device { /* currently active master for this device. Protected by master_mutex */ struct drm_master *master; - atomic_t unplugged; /**< Flag whether dev is dead */ + /** + * @unplugged: + * + * Flag to tell if the device has been unplugged. + * See drm_dev_enter() and drm_dev_is_unplugged(). + */ + bool unplugged; + struct inode *anon_inode; /**< inode for private address-space */ char *unique; /**< unique name of the device */ /*@} */ diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h index d23dcdd1bd95..7e545f5f94d3 100644 --- a/include/drm/drm_drv.h +++ b/include/drm/drm_drv.h @@ -624,6 +624,8 @@ void drm_dev_get(struct drm_device *dev); void drm_dev_put(struct drm_device *dev); void drm_dev_unref(struct drm_device *dev); void drm_put_dev(struct drm_device *dev); +bool drm_dev_enter(struct drm_device *dev, int *idx); +void drm_dev_exit(int idx); void drm_dev_unplug(struct drm_device *dev); /** @@ -635,11 +637,16 @@ void drm_dev_unplug(struct drm_device *dev); * unplugged, these two functions guarantee that any store before calling * drm_dev_unplug() is visible to callers of this function after it completes */ -static inline int drm_dev_is_unplugged(struct drm_device *dev) +static inline bool drm_dev_is_unplugged(struct drm_device *dev) { - int ret = atomic_read(&dev->unplugged); - smp_rmb(); - return ret; + int idx; + + if (drm_dev_enter(dev, &idx)) { + drm_dev_exit(idx); + return false; + } + + return true; }