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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 524CCC83F12 for ; Tue, 29 Aug 2023 02:34:31 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 8E44310E38B; Tue, 29 Aug 2023 02:34:30 +0000 (UTC) Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by gabe.freedesktop.org (Postfix) with ESMTPS id B5E7910E38B; Tue, 29 Aug 2023 02:34:28 +0000 (UTC) Received: from [192.168.2.140] (109-252-153-31.dynamic.spd-mgts.ru [109.252.153.31]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id CBA5D66071DC; Tue, 29 Aug 2023 03:34:25 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693276467; bh=zCen/op7wjIViqDfv+0NVKrUFjfQTD9AYmbvMVtk7Kw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=W1tbxb/5VsSOn3rRGQU03/q8ShP/ocfyo846hcjEpv+yPGEcRkyz4bAw9Rq1AsIC2 i2AZ4LVCCrkKv0jndNrxNLJB2i8Y4P+afaIybxKqYR1YQM0B+oPZAtR3rdvRnWot+4 zu1AywW6h7UeEBhKnHVX6D+l6DB77pJs/BPy/yd61CeOlns7YZWm6H8lxj6EfAm9Hj fSVJpZXVDAFf9pcc76h5n/fFLIJhR+f7aNsor+uEA0HjNb8CbxAk25S0G1xQEVvDD6 E/ymlXw5rDXqpAzHh1kWcq0CAuFB/KxxkBHsQk23XN8DYxhAtDpgC87GuffSGljg+h Wp3YHLWy0rpfw== Message-ID: <01930e66-cba2-5d81-7f46-d46907bdd300@collabora.com> Date: Tue, 29 Aug 2023 05:34:23 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Content-Language: en-US To: Boris Brezillon References: <20230827175449.1766701-1-dmitry.osipenko@collabora.com> <20230827175449.1766701-18-dmitry.osipenko@collabora.com> <20230828121239.78a180e6@collabora.com> From: Dmitry Osipenko In-Reply-To: <20230828121239.78a180e6@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Intel-gfx] [PATCH v15 17/23] drm/shmem-helper: Add and use drm_gem_shmem_resv_assert_held() helper X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Emma Anholt , Peter Zijlstra , dri-devel@lists.freedesktop.org, Gurchetan Singh , Gerd Hoffmann , kernel@collabora.com, Will Deacon , David Airlie , Steven Price , intel-gfx@lists.freedesktop.org, Daniel Vetter , Boqun Feng , Maxime Ripard , Melissa Wen , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Chia-I Wu , Qiang Yu , Thomas Zimmermann , =?UTF-8?Q?Christian_K=c3=b6nig?= Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 8/28/23 13:12, Boris Brezillon wrote: > 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. It's not only drm_gem_shmem_free_pages(), but any drm-shmem function that drivers may use in the GEM's freeing callback. For example, panfrost_gem_free_object() may unpin shmem BO and then do drm_gem_shmem_free(). -- Best regards, Dmitry