From bee330f3d67273a68dcb99f59480d59553c008b2 Mon Sep 17 00:00:00 2001 From: Noralf Trønnes Date: Wed, 28 Mar 2018 10:38:35 +0300 Subject: drm: Use srcu to protect drm_device.unplugged MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Oleksandr Andrushchenko Reviewed-by: Oleksandr Andrushchenko Tested-by: Oleksandr Andrushchenko Cc: intel-gfx@lists.freedesktop.org Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/1522222715-11814-1-git-send-email-andr2000@gmail.com --- drivers/gpu/drm/drm_drv.c | 54 ++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 49 insertions(+), 5 deletions(-) (limited to 'drivers/gpu/drm/drm_drv.c') 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); -- cgit v1.2.3