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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dg4SjD1PSzDobzlYvOGEcqCLF1x2F5Gtj3yeD5z4z0LNmlBZ7nPp5hO2RqdB+RZaY 3aA/b/CaqZrwzgxDqBjqryJ2fSqEHIT+vlwMgvlO1glx3hENc08EwGPqdsfohZX68b Vw2OzQI5gyXo4L8Xnl3hx1gXhHW11NBIbb32oRoA= Date: Thu, 7 May 2026 11:20:41 +0100 From: Liviu Dudau To: Boris Brezillon Cc: Steven Price , Dmitry Osipenko , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Akash Goel , Chia-I Wu , Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Jessica Zhang , Sean Paul , Marijn Suijten , linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] drm/gem: Stop exposing the racy/unsafe drm_gem_lru_remove() helper Message-ID: References: <20260506-panthor-shrinker-fixes-v1-0-e7721526de96@collabora.com> <20260506-panthor-shrinker-fixes-v1-3-e7721526de96@collabora.com> Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260506-panthor-shrinker-fixes-v1-3-e7721526de96@collabora.com> On Wed, May 06, 2026 at 02:16:28PM +0200, Boris Brezillon wrote: > The only place where it's safe to call drm_gem_lru_remove() is when > we know the drm_gem_object::lru field can't be concurrently updated, > which we know is the case when the drm_gem_object is destroyed. > > Rather than trying to make that safe, let's kill the function and inline > its content in drm_gem_object_release(). > > Signed-off-by: Boris Brezillon > Reviewed-by: Chia-I Wu Reviewed-by: Liviu Dudau Best regards, Liviu > --- > drivers/gpu/drm/drm_gem.c | 49 +++++++++++++++++------------------------------ > include/drm/drm_gem.h | 1 - > 2 files changed, 18 insertions(+), 32 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > index 97cf63de0112..b6df4f62f7b5 100644 > --- a/drivers/gpu/drm/drm_gem.c > +++ b/drivers/gpu/drm/drm_gem.c > @@ -1108,6 +1108,15 @@ drm_gem_release(struct drm_device *dev, struct drm_file *file_private) > idr_destroy(&file_private->object_idr); > } > > +static void > +drm_gem_lru_remove_locked(struct drm_gem_object *obj) > +{ > + obj->lru->count -= obj->size >> PAGE_SHIFT; > + WARN_ON(obj->lru->count < 0); > + list_del(&obj->lru_node); > + obj->lru = NULL; > +} > + > /** > * drm_gem_object_release - release GEM buffer object resources > * @obj: GEM buffer object > @@ -1124,7 +1133,15 @@ drm_gem_object_release(struct drm_gem_object *obj) > drm_gem_private_object_fini(obj); > > drm_gem_free_mmap_offset(obj); > - drm_gem_lru_remove(obj); > + > + /* If the object refcount drops to zero, it means no one can change > + * the LRU it's inserted into, so it's safe to dereference > + * drm_gem_object::lru without the drm_gem_lru::lock held. > + */ > + if (obj->lru) { > + guard(mutex)(obj->lru->lock); > + drm_gem_lru_remove_locked(obj); > + } > } > EXPORT_SYMBOL(drm_gem_object_release); > > @@ -1552,36 +1569,6 @@ drm_gem_lru_init(struct drm_gem_lru *lru, struct mutex *lock) > } > EXPORT_SYMBOL(drm_gem_lru_init); > > -static void > -drm_gem_lru_remove_locked(struct drm_gem_object *obj) > -{ > - obj->lru->count -= obj->size >> PAGE_SHIFT; > - WARN_ON(obj->lru->count < 0); > - list_del(&obj->lru_node); > - obj->lru = NULL; > -} > - > -/** > - * drm_gem_lru_remove - remove object from whatever LRU it is in > - * > - * If the object is currently in any LRU, remove it. > - * > - * @obj: The GEM object to remove from current LRU > - */ > -void > -drm_gem_lru_remove(struct drm_gem_object *obj) > -{ > - struct drm_gem_lru *lru = obj->lru; > - > - if (!lru) > - return; > - > - mutex_lock(lru->lock); > - drm_gem_lru_remove_locked(obj); > - mutex_unlock(lru->lock); > -} > -EXPORT_SYMBOL(drm_gem_lru_remove); > - > /** > * drm_gem_lru_move_tail_locked - move the object to the tail of the LRU > * > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h > index 86f5846154f7..d527df98d142 100644 > --- a/include/drm/drm_gem.h > +++ b/include/drm/drm_gem.h > @@ -611,7 +611,6 @@ int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev, > u32 handle, u64 *offset); > > void drm_gem_lru_init(struct drm_gem_lru *lru, struct mutex *lock); > -void drm_gem_lru_remove(struct drm_gem_object *obj); > void drm_gem_lru_move_tail_locked(struct drm_gem_lru *lru, struct drm_gem_object *obj); > void drm_gem_lru_move_tail(struct drm_gem_lru *lru, struct drm_gem_object *obj); > unsigned long > > -- > 2.54.0 > -- ==================== | I would like to | | fix the world, | | but they're not | | giving me the | \ source code! / --------------- ¯\_(ツ)_/¯