From 03a9606e7feef902979bbc0601d6d93e764f251d Mon Sep 17 00:00:00 2001 From: Noralf Trønnes Date: Mon, 6 May 2019 20:01:30 +0200 Subject: drm/fb-helper: Avoid race with DRM userspace MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit drm_fb_helper_is_bound() is used to check if DRM userspace is in control. This is done by looking at the fb on the primary plane. By the time fb-helper gets around to committing, it's possible that the facts have changed. Avoid this race by holding the drm_device->master_mutex lock while committing. When DRM userspace does its first open, it will now wait until fb-helper is done. The helper will stay away if there's a master. Two igt tests fail with the new 'bail out if master' rule. Work around this by relaxing this rule for drm_fb_helper_restore_fbdev_mode_unlocked() until the tests have been fixed. Add todo entry for this. Locking rule: Always take the fb-helper lock first. v5: drm_fb_helper_restore_fbdev_mode_unlocked(): Use restore_fbdev_mode_force() v2: - Remove drm_fb_helper_is_bound() (Daniel Vetter) - No need to check fb_helper->dev->master in drm_fb_helper_single_fb_probe(), restore_fbdev_mode() has the check. Suggested-by: Daniel Vetter Signed-off-by: Noralf Trønnes Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20190506180139.6913-3-noralf@tronnes.org --- drivers/gpu/drm/drm_auth.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'drivers/gpu/drm/drm_auth.c') diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 22c7a104b802..bf98402f3210 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -351,3 +351,23 @@ void drm_master_put(struct drm_master **master) *master = NULL; } EXPORT_SYMBOL(drm_master_put); + +/* Used by drm_client and drm_fb_helper */ +bool drm_master_internal_acquire(struct drm_device *dev) +{ + mutex_lock(&dev->master_mutex); + if (dev->master) { + mutex_unlock(&dev->master_mutex); + return false; + } + + return true; +} +EXPORT_SYMBOL(drm_master_internal_acquire); + +/* Used by drm_client and drm_fb_helper */ +void drm_master_internal_release(struct drm_device *dev) +{ + mutex_unlock(&dev->master_mutex); +} +EXPORT_SYMBOL(drm_master_internal_release); -- cgit v1.2.3