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 1C048C83F12 for ; Mon, 28 Aug 2023 10:13:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230353AbjH1KNE (ORCPT ); Mon, 28 Aug 2023 06:13:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230406AbjH1KMu (ORCPT ); Mon, 28 Aug 2023 06:12:50 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D357B10C for ; Mon, 28 Aug 2023 03:12:44 -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 C03AE6607181; Mon, 28 Aug 2023 11:12:42 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693217563; bh=8VxF/Zh3lcDahMBvxQgvdgpueUTKgY5p3OuJRZFv2TI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=degu/FMjBsTpOjLuM74t3Lew4KY74VhueEVgDUPC8dNb5RXlvt9bqrW4oFqRXlVck rdnBIawv7jS5BTtN9Kn3EtUCL7nbianiihDTPAteaWT4zy/pdVb+w1T/RgU2ORbky3 8MVFUGGNyF0xHtueLkSYFIE8VzdsClHeildj8WER5U8dIQEVVTAmfSg6EWQv7xsCJp QDKCX0D0b6uzweZK68Uj2eaaoVML5eX3x/kgeh85BeQcOseq4qm827inHHwEv6/JRa p/tIXOaTgz6ILjJsb1ZabJqfdjD2bekXIMO3VXDKvV8g1UrkXBMCIc9dlyMNBWPedX aqvpnqF5euzzQ== Date: Mon, 28 Aug 2023 12:12:39 +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 , Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org Subject: Re: [PATCH v15 17/23] drm/shmem-helper: Add and use drm_gem_shmem_resv_assert_held() helper Message-ID: <20230828121239.78a180e6@collabora.com> In-Reply-To: <20230827175449.1766701-18-dmitry.osipenko@collabora.com> References: <20230827175449.1766701-1-dmitry.osipenko@collabora.com> <20230827175449.1766701-18-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 Sun, 27 Aug 2023 20:54:43 +0300 Dmitry Osipenko wrote: > In a preparation of adding drm-shmem memory shrinker, move all reservation > locking lockdep checks to use new drm_gem_shmem_resv_assert_held() that > will resolve spurious lockdep warning about wrong locking order vs > fs_reclam code paths during freeing of shmem GEM, where lockdep isn't > aware that it's impossible to have locking contention with the fs_reclam > at this special time. > > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 37 +++++++++++++++++--------- > 1 file changed, 25 insertions(+), 12 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index d96fee3d6166..ca5da976aafa 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -128,6 +128,23 @@ 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_resv_assert_held(struct drm_gem_shmem_object *shmem) > +{ > + /* > + * Destroying the object is a special case.. drm_gem_shmem_free() > + * calls many things that WARN_ON if the obj lock is not held. But > + * acquiring the obj lock in drm_gem_shmem_free() can cause a locking > + * order inversion between reservation_ww_class_mutex and fs_reclaim. > + * > + * 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, we pretend it is already locked. > + */ > + if (kref_read(&shmem->base.refcount)) > + drm_gem_shmem_resv_assert_held(shmem); > +} > + > /** > * drm_gem_shmem_free - Free resources associated with a shmem GEM object > * @shmem: shmem GEM object to free > @@ -142,8 +159,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > if (obj->import_attach) { > drm_prime_gem_destroy(obj, shmem->sgt); > } else if (!shmem->imported_sgt) { > - dma_resv_lock(shmem->base.resv, NULL); > - > drm_WARN_ON(obj->dev, kref_read(&shmem->vmap_use_count)); > > if (shmem->sgt) { > @@ -156,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > drm_gem_shmem_put_pages_locked(shmem); AFAICT, drm_gem_shmem_put_pages_locked() is the only function that's called in the free path and would complain about resv-lock not being held. I think I'd feel more comfortable if we were adding a drm_gem_shmem_free_pages() function that did everything drm_gem_shmem_put_pages_locked() does except for the lock_held() check and the refcount dec, and have it called here (and in drm_gem_shmem_put_pages_locked()). This way we can keep using dma_resv_assert_held() instead of having our own variant. > > drm_WARN_ON(obj->dev, kref_read(&shmem->pages_use_count)); > - > - dma_resv_unlock(shmem->base.resv); > } > > drm_gem_object_release(obj); > @@ -170,7 +183,7 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) > struct drm_gem_object *obj = &shmem->base; > struct page **pages; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (kref_get_unless_zero(&shmem->pages_use_count)) > return 0; > @@ -228,7 +241,7 @@ static void drm_gem_shmem_kref_release_pages(struct kref *kref) > */ > void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) > { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > kref_put(&shmem->pages_use_count, drm_gem_shmem_kref_release_pages); > } > @@ -252,7 +265,7 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem) > { > int ret; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (kref_get_unless_zero(&shmem->pages_pin_count)) > return 0; > @@ -276,7 +289,7 @@ static void drm_gem_shmem_kref_unpin_pages(struct kref *kref) > > static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem) > { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > kref_put(&shmem->pages_pin_count, drm_gem_shmem_kref_unpin_pages); > } > @@ -357,7 +370,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem, > } else { > pgprot_t prot = PAGE_KERNEL; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (kref_get_unless_zero(&shmem->vmap_use_count)) { > iosys_map_set_vaddr(map, shmem->vaddr); > @@ -426,7 +439,7 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem, > if (obj->import_attach) { > dma_buf_vunmap(obj->import_attach->dmabuf, map); > } else { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > kref_put(&shmem->vmap_use_count, drm_gem_shmem_kref_vunmap); > } > > @@ -462,7 +475,7 @@ drm_gem_shmem_create_with_handle(struct drm_file *file_priv, > */ > int drm_gem_shmem_madvise_locked(struct drm_gem_shmem_object *shmem, int madv) > { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (shmem->madv >= 0) > shmem->madv = madv; > @@ -478,7 +491,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem) > struct drm_gem_object *obj = &shmem->base; > struct drm_device *dev = obj->dev; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > drm_WARN_ON(obj->dev, !drm_gem_shmem_is_purgeable(shmem)); >