Hi Am 17.05.23 um 19:04 schrieb Matthew Auld:
On 17/05/2023 17:21, Thomas Zimmermann wrote:Hi Am 17.05.23 um 17:22 schrieb Matthew Auld:In mutex_init() lockdep seems to identify a lock by defining a static key for each lock class. However if we wrap the whole thing in a function the static key will be the same for everything calling that function, which looks to be the case for drmm_mutex_init(). This then results in impossible lockdep splats since lockdep thinks completely unrelated locks are the same lock class. The other issue is that when looking at splats we lose the actual lock name, where instead of seeing something like xe->mem_access.lock for the name, we just see something generic like lock#8. Attempt to fix this by converting drmm_mutex_init() into a macro, which should ensure that mutex_init() behaves as expected.If that's what is required, then OK. But even with your commit mesage, I find it entirely non-obvious what the problem is. Isn't there a way to annotate drmm_mutex_init() so that lockdep treats it like a regular mutex_init()?AFAICT the issue is that with the existing drmm_mutex_init() we basically end up generating:int drmm_mutex_init(struct drm_device *dev, struct mutex *lock) { static struct lock_class_key __key; __mutex_init((lock), "lock", &__key); .... }I think the special static __key is what lockdep uses to identify a lock class, so every time we call drmm_mutex_init() we should expect a different key. However since this is just a normal function the key will be created once and then all callers use the same key. For example, if you print mutex->depmap.key you will get the same pointer underneath for different drmm_mutex_init callers. And then ofc lockdep gets really confused.Turning it into a macro ensures that each drmm_mutex_init() generates a different "static struct lock_class_key __key" for each invocation, which looks to be inline with what mutex_init() wants.
OK, thanks a lot for explaining. Best regards Thomas
I'm not sure if there a better way to solve this...Best regards ThomasReported-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx> Fixes: e13f13e039dc ("drm: Add DRM-managed mutex_init()") Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> Cc: Jocelyn Falempe <jfalempe@xxxxxxxxxx> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx> --- drivers/gpu/drm/drm_managed.c | 26 -------------------------- include/drm/drm_managed.h | 23 ++++++++++++++++++++++- 2 files changed, 22 insertions(+), 27 deletions(-)diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.cindex 4cf214de50c4..71c49819a7a2 100644 --- a/drivers/gpu/drm/drm_managed.c +++ b/drivers/gpu/drm/drm_managed.c @@ -263,29 +263,3 @@ void drmm_kfree(struct drm_device *dev, void *data) free_dr(dr_match); } EXPORT_SYMBOL(drmm_kfree); - -static void drmm_mutex_release(struct drm_device *dev, void *res) -{ - struct mutex *lock = res; - - mutex_destroy(lock); -} - -/** - * drmm_mutex_init - &drm_device-managed mutex_init() - * @dev: DRM device - * @lock: lock to be initialized - * - * Returns: - * 0 on success, or a negative errno code otherwise. - *- * This is a &drm_device-managed version of mutex_init(). The initialized- * lock is automatically destroyed on the final drm_dev_put(). - */ -int drmm_mutex_init(struct drm_device *dev, struct mutex *lock) -{ - mutex_init(lock); - - return drmm_add_action_or_reset(dev, drmm_mutex_release, lock); -} -EXPORT_SYMBOL(drmm_mutex_init); diff --git a/include/drm/drm_managed.h b/include/drm/drm_managed.h index 359883942612..01f977e91933 100644 --- a/include/drm/drm_managed.h +++ b/include/drm/drm_managed.h@@ -105,6 +105,27 @@ char *drmm_kstrdup(struct drm_device *dev, const char *s, gfp_t gfp);void drmm_kfree(struct drm_device *dev, void *data); -int drmm_mutex_init(struct drm_device *dev, struct mutex *lock);+static inline void __drmm_mutex_release(struct drm_device *dev, void *res)+{ + struct mutex *lock = res; + + mutex_destroy(lock); +} + +/** + * drmm_mutex_init - &drm_device-managed mutex_init() + * @dev: DRM device + * @lock: lock to be initialized + * + * Returns: + * 0 on success, or a negative errno code otherwise. + *+ * This is a &drm_device-managed version of mutex_init(). The initialized+ * lock is automatically destroyed on the final drm_dev_put(). + */ +#define drmm_mutex_init(dev, lock) ({ \ + mutex_init(lock); \+ drmm_add_action_or_reset(dev, __drmm_mutex_release, lock); \+}) \ #endif
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
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