Re: [Intel-gfx] [PATCH v4 1/2] drm: Use srcu to protect drm_device.unplugged
On Wed, Mar 28, 2018 at 09:47:40AM +0300, Oleksandr Andrushchenko wrote: > From: Noralf Trønnes > > 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 > Signed-off-by: Noralf Trønnes > Reviewed-by: Oleksandr Andrushchenko > Tested-by: Oleksandr Andrushchenko > Cc: intel-...@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 > #include > #include > +#include > > #include > #include > @@ -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 d2
[PATCH v4 1/2] drm: Use srcu to protect drm_device.unplugged
From: Noralf Trønnes 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 Signed-off-by: Noralf Trønnes Reviewed-by: Oleksandr Andrushchenko Tested-by: Oleksandr Andrushchenko Cc: intel-...@lists.freedesktop.org --- 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 #include #include +#include #include #include @@ -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, t