From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1534EE6425 for ; Fri, 15 Sep 2023 07:28:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232282AbjIOH20 (ORCPT ); Fri, 15 Sep 2023 03:28:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51260 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232251AbjIOH2Y (ORCPT ); Fri, 15 Sep 2023 03:28:24 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CC861FD2 for ; Fri, 15 Sep 2023 00:27:55 -0700 (PDT) Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by madras.collabora.co.uk (Postfix) with ESMTPSA id 1721B6607326; Fri, 15 Sep 2023 08:27:53 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1694762873; bh=YMYjtrrkf8T9IjXqAxdfDX4QRVZqiwOsrCaZpTx70xg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ToXMSRFiOqX74YLFMRGj6dsDbWl7RvH/a5lC+ySzYZPEgPmEAxRjkn5nafDVeyFoS /tmOKxFF3h/4iHcLnytcSrh9Yk+nXka8vSaM7fjv+x5q9ZE7F15Rgt5XJioNHjIUc1 gC3vrHXNDfoqRJ3h5XHw9cS+GnHCn9IyzPzSGTAUINgmJNrZx7xf0e8VxbrApbP1xy SO8GkscB8VV79QVdopjmWE0Ney+pUN97ptNBp8m5acEG5UateTRpHOhRuqtNKeOYFU +OKmaQr/Yfs80o9d9R3zWa+Cv63jc4oHlBTaN51v3B1RaPAsPUX50LjfIExOCt8OtM 5XI/RVmAnwwZA== Date: Fri, 15 Sep 2023 09:27:50 +0200 From: Boris Brezillon To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?UTF-8?B?S8O2bmln?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v17 12/18] drm/shmem-helper: Prepare drm_gem_shmem_free() to shrinker addition Message-ID: <20230915092750.17e88b23@collabora.com> In-Reply-To: <20230914232721.408581-13-dmitry.osipenko@collabora.com> References: <20230914232721.408581-1-dmitry.osipenko@collabora.com> <20230914232721.408581-13-dmitry.osipenko@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 15 Sep 2023 02:27:15 +0300 Dmitry Osipenko wrote: > Prepare drm_gem_shmem_free() to addition of memory shrinker support > to drm-shmem by adding and using variant of put_pages() that doesn't > touch reservation lock. Reservation shouldn't be touched because lockdep > will trigger a bogus warning about locking contention with fs_reclaim > code paths that can't happen during the time when GEM is freed and > lockdep doesn't know about that. > > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 55 +++++++++++++++++--------- > 1 file changed, 37 insertions(+), 18 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 8a8eab4d0332..4959f51b647a 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -128,6 +128,41 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_create); > > +static void > +__drm_gem_shmem_release_pages(struct drm_gem_shmem_object *shmem) Could we find more descriptive names to replace those __ prefixes? drm_gem_shmem_free_pages(), drm_gem_shmem_drop_pages()? > +{ > + struct drm_gem_object *obj = &shmem->base; > + > +#ifdef CONFIG_X86 > + if (shmem->map_wc) > + set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT); > +#endif > + > + drm_gem_put_pages(obj, shmem->pages, > + shmem->pages_mark_dirty_on_put, > + shmem->pages_mark_accessed_on_put); > + shmem->pages = NULL; > +} > + > +static void > +__drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem) Maybe drm_gem_shmem_put_pages_no_lock_check()? But honestly, I'm not sure we want to make it a function since it's only going to be needed in drm_gem_shmem_free(). I think we can just inline if (refcount_dec_and_test(&shmem->pages_use_count)) __drm_gem_shmem_release_pages(shmem); there. > +{ > + /* > + * Destroying the object is a special case. Acquiring the obj > + * lock in drm_gem_shmem_put_pages_locked() can cause a locking > + * order inversion between reservation_ww_class_mutex and fs_reclaim > + * when called from drm_gem_shmem_free(). > + * > + * This deadlock is not actually possible, because no one should > + * be already holding the lock when drm_gem_shmem_free() is called. > + * Unfortunately lockdep is not aware of this detail. So when the > + * refcount drops to zero, make sure that the reservation lock > + * isn't touched here. > + */ > + if (refcount_dec_and_test(&shmem->pages_use_count)) > + __drm_gem_shmem_release_pages(shmem); > +} > + > /** > * drm_gem_shmem_free - Free resources associated with a shmem GEM object > * @shmem: shmem GEM object to free > @@ -142,8 +177,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > if (obj->import_attach) { > drm_prime_gem_destroy(obj, shmem->sgt); > } else { > - dma_resv_lock(shmem->base.resv, NULL); > - > drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count)); > > if (shmem->sgt) { > @@ -153,11 +186,9 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > kfree(shmem->sgt); > } > if (shmem->pages) > - drm_gem_shmem_put_pages_locked(shmem); > + __drm_gem_shmem_put_pages(shmem); > > drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count)); > - > - dma_resv_unlock(shmem->base.resv); > } > > drm_gem_object_release(obj); > @@ -207,21 +238,9 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) > */ > void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) > { > - struct drm_gem_object *obj = &shmem->base; > - > dma_resv_assert_held(shmem->base.resv); > > - if (refcount_dec_and_test(&shmem->pages_use_count)) { > -#ifdef CONFIG_X86 > - if (shmem->map_wc) > - set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT); > -#endif > - > - drm_gem_put_pages(obj, shmem->pages, > - shmem->pages_mark_dirty_on_put, > - shmem->pages_mark_accessed_on_put); > - shmem->pages = NULL; > - } > + __drm_gem_shmem_put_pages(shmem); > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked); >