From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8AD5B47CC80; Wed, 6 May 2026 15:40:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778082044; cv=none; b=j6mVolfHCm5yXbCgigjVJZKxC6IQuag014mm9tXohp2a12YJF4dWBjX57OKjeOAT+beWmZDPZRsYCYtPnfaaT3QVXpsXztY8aD0lXC2SmiXEutmESbEVp7+moEFyFeIb+X2WTFesmakrpwY+emEXSETtZE40Ax/DoLNYmkSf2sw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778082044; c=relaxed/simple; bh=dOuepOxYrvpC0eOxRlco60j01LRxjiAn+sxvV1US3cM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eZI/mGSkpjv3zcZz0q/IJpA478kOkOB9+CFmipPCyEw74pNbUZj7b/PZ4C3u1Dgxrw+HUI2pV7Ly8qyHWk3oqHQP+BSOeOIRyAEpNjmRm/GwWzQJjz3T8FBVCamuJ5ncBdg0vvQ/YNRN6FVsETbrXs2blrLXa57V2gRh4QQUxyg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=nTulg/TG; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="nTulg/TG" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D7146302F; Wed, 6 May 2026 08:40:27 -0700 (PDT) Received: from [10.57.69.49] (unknown [10.57.69.49]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F63E3F7B4; Wed, 6 May 2026 08:40:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1778082033; bh=dOuepOxYrvpC0eOxRlco60j01LRxjiAn+sxvV1US3cM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nTulg/TGSqDYhnUd1XNCVDDgbDaLvlULG7zZKlbySv2F/KJYCp6CdpgdIUkCCUhTx R/t2roT6VmnjoOLMzGDJzQ+kiexzat/4pZZkltZPljC3hlwMasZ6b+8FveS4oFvVGZ BIl9nKaIifMIzdLKtb5qNSQY8m95YO2voLATZqm8= Message-ID: Date: Wed, 6 May 2026 16:40:23 +0100 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/3] drm/gem: Stop exposing the racy/unsafe drm_gem_lru_remove() helper To: Boris Brezillon , Liviu Dudau , Dmitry Osipenko Cc: 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 References: <20260506-panthor-shrinker-fixes-v1-0-e7721526de96@collabora.com> <20260506-panthor-shrinker-fixes-v1-3-e7721526de96@collabora.com> From: Steven Price Content-Language: en-GB In-Reply-To: <20260506-panthor-shrinker-fixes-v1-3-e7721526de96@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 06/05/2026 13:16, 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: Steven Price > --- > 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 >