From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender6-op-o11.zoho.com (sender6-op-o11.zoho.com [165.173.180.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EFC4B36BCED for ; Wed, 14 Oct 2026 21:04:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=165.173.180.11 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792011846; cv=pass; b=XJDQnweImPrVxQYl1F/I1d4+OKKzhNQlNZ6ChU3NggGNoq61oZO6xqOu/VZtDRqmqlmNHm4x10ckFnGaMvWxu1s76XAuTjdIgVDCBpyonA6tnpJ+rtUtWwLG7asqAgYvieUB6/BiP8pgJEkZJMO9iNpYmgZk1y5bU0Gzrf7X/Pk= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792011846; c=relaxed/simple; bh=hQ+3ixWZSWCaB7DIMnxiLTYYC/EatAKsu6DQudQfNPk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GsRFnY1c27eBS7fyLItPjPpLJx/JM98guW3sIlUxzZ2/S1IUkrTu7QyZ/vnmRJzfDA8g90T82nGGcbJ7RltBQ7qjP0F3eCLN60fg8MPl47RXkonF9cMX85Jh66ieVtaQPyY40LXIHuyCo/y2JPb6QE6ekzWqetZX+SzqE8g2yIM= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (1024-bit key) header.d=collabora.com header.i=dmitry.osipenko@collabora.com header.b=P9HcgNrw; arc=pass smtp.client-ip=165.173.180.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=collabora.com header.i=dmitry.osipenko@collabora.com header.b="P9HcgNrw" ARC-Seal: i=1; a=rsa-sha256; t=1792011819; cv=none; d=zohomail.com; s=zohoarc; b=DS24hgiAZTMXMuMA77Epom4iA6pRdEZtBw2kY2Lg8ejFdx1x15KQbXu3UneKDX5GiUMIdhuw36iidKOrihDT1A6688TZ4lq38fY5kB6fNaSxd+W+AfqdycNCmYfNCndqKf9TgwXTDBqC4Ksw8qnS168jSKlzLhJDUwuOZodmkTc= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1792011819; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:Subject:Subject:To:To:Message-Id:Reply-To; bh=TO/lIMPRy42IA1901iUdgP3yZWKR6dl0nOUutKb0wR0=; b=hX/dfSJOhNxAzG7C52j8ZEDkZYiP2n1eDOAUzMukHHAOfA74lc1p3Dk1Y+P8wdRUBwLckObH8zw8EZIbuZGSSUi62Vr/xQTihA5h0JL4eSOUNMkx9afhpAlAhYIbhvrokv6mLW3Leha7Oy9CfNDDqo0ARH2C0Gd7vlO7Tphw/j4= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=dmitry.osipenko@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1792011819; s=zohomail; d=collabora.com; i=dmitry.osipenko@collabora.com; h=Message-ID:Date:Date:MIME-Version:Subject:Subject:To:To:Cc:Cc:From:From:In-Reply-To:Content-Type:Content-Transfer-Encoding:Message-Id:Reply-To; bh=TO/lIMPRy42IA1901iUdgP3yZWKR6dl0nOUutKb0wR0=; b=P9HcgNrwgmif3VkXwO9nQRNUfoaIjEFHmlKeEj5rYoKCVFNn1siEuiStzfE1XwX9 CSlYj3XCDJQtKKGrD4CBFFS1KnBfxkYEx+PVVEXFOH3PxVsI5583uPhRv6sA8si0/5o rn4LLvQdMXSbYLz7sNYZuChb5eO2pC5Afyd0IqIE= Received: by smtp.zohomail.com with SMTPS id 1792011817897320.64940566528196; Wed, 14 Oct 2026 14:03:37 -0700 (PDT) Message-ID: <8e193dd9-4ceb-4bd0-a28f-f4af084b73e8@collabora.com> Date: Thu, 15 Oct 2026 00:03:32 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/virtio: Destroy obj_restore_lock on the final drm_dev_put() To: Abhin Parekadan Jose Cc: Gerd Hoffmann , David Airlie , Gurchetan Singh , Chia-I Wu , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Simona Vetter , Dongwon Kim , dri-devel@lists.freedesktop.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot+3590d97d8a586fa955c2@syzkaller.appspotmail.com References: <20260929070714.169412-1-abhinjoses@gmail.com> <537679fc-8aea-472f-a7af-b15bd3cf27fd@collabora.com> Content-Language: en-US From: Dmitry Osipenko In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ZohoMailClient: External On 10/14/26 22:53, Abhin Parekadan Jose wrote: > On Wed, Oct 14, 2026 at 01:16:57AM +0300, Dmitry Osipenko wrote: >> On 10/12/26 08:44, Abhin Parekadan Jose wrote: >>> Gentle ping on this fix for the syzbot report. >>> >>> Dmitry, Gerd, do you have a preference between moving mutex_destroy() >>> to virtio_gpu_release() (this patch) and using drmm_mutex_init()? I can >>> send a v2 with the other option if you prefer it. >>> >>> Thanks, >>> Abhin >>> >>> On Tue, Sep 29, 2026 at 07:07:14AM +0000, Abhin Parekadan Jose wrote: >>>> virtio_gpu_deinit() calls mutex_destroy() on obj_restore_lock, but >>>> deinit runs from virtio_gpu_remove() at unbind or PCI remove, and GEM >>>> objects can outlive that. An open /dev/fb0 keeps the fbdev buffer >>>> alive, and the fbdev DRM client holds a drm_device reference. When the >>>> fd is finally closed, the buffer is freed and takes the destroyed lock: >>>> >>>> fb_release() >>>> drm_fbdev_shmem_fb_destroy() >>>> drm_client_buffer_delete() >>>> virtio_gpu_free_object() >>>> virtio_gpu_remove_from_restore_list() >>>> mutex_lock(&vgdev->obj_restore_lock) >>>> >>>> DEBUG_LOCKS_WARN_ON(lock->magic != lock) >>>> WARNING: kernel/locking/mutex.c:625 at __mutex_lock+0xf2c/0x12ec >>>> >>>> virtio_gpu_deinit() should only do hardware teardown in this case >>>> related virtio, its queues and others. Software state that GEM callbacks >>>> still use belongs in virtio_gpu_release(), which runs on the final >>>> drm_dev_put(). >>>> >>>> There are two equivalent ways to tie the mutex lifetime to the >>>> drm_device: >>>> >>>> 1) Move mutex_destroy() from virtio_gpu_deinit() to the end of >>>> virtio_gpu_release(). This is what this patch does. It is the >>>> smallest change and keeps the teardown next to the rest of the >>>> final-put software cleanup. >>>> >>>> 2) Initialise the lock with drmm_mutex_init() (checking its return >>>> value) and drop mutex_destroy() from virtio_gpu_deinit(), so DRM's >>>> managed release destroys it. This also covers the virtio_gpu_init() >>>> error path, where release returns early because dev_private is >>>> NULL. Skipping mutex_destroy() there is harmless, since it only >>>> matters for mutex debugging. >>>> >>>> Either fix removes the WARN. Option 1 is sent as the smaller change, >>>> and option 2 can be done instead if preferred. >>>> >>>> Reproduced on arm64 QEMU (-device virtio-gpu-pci) with DEBUG_MUTEXES >>>> and PROVE_LOCKING: open /dev/fb0, write 1 to >>>> /sys/bus/pci/devices/0000:00:01.0/remove, then close the fd. With this >>>> patch the WARN is gone, and rebinding brings back /dev/fb0 and >>>> /dev/dri/card0. >>>> >>>> Fixes: 54a970048296 ("drm/virtio: Add support for saving and restoring virtio_gpu_objects") >>>> Reported-by: syzbot+3590d97d8a586fa955c2@syzkaller.appspotmail.com >>>> Closes: https://syzkaller.appspot.com/bug?extid=3590d97d8a586fa955c2 >>>> Assisted-by: LLM >>>> Signed-off-by: Abhin Parekadan Jose >>>> --- >>>> drivers/gpu/drm/virtio/virtgpu_kms.c | 3 ++- >>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c >>>> index 1d4d3bf46a20..0ec755c35050 100644 >>>> --- a/drivers/gpu/drm/virtio/virtgpu_kms.c >>>> +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c >>>> @@ -354,7 +354,6 @@ void virtio_gpu_deinit(struct drm_device *dev) >>>> virtio_reset_device(vgdev->vdev); >>>> virtio_gpu_reclaim_vbufs(vgdev); >>>> vgdev->vdev->config->del_vqs(vgdev->vdev); >>>> - mutex_destroy(&vgdev->obj_restore_lock); >>>> } >>>> >>>> void virtio_gpu_release(struct drm_device *dev) >>>> @@ -370,6 +369,8 @@ void virtio_gpu_release(struct drm_device *dev) >>>> >>>> if (vgdev->has_host_visible) >>>> drm_mm_takedown(&vgdev->host_visible_mm); >>>> + >>>> + mutex_destroy(&vgdev->obj_restore_lock); >>>> } >>>> >>>> int virtio_gpu_driver_open(struct drm_device *dev, struct drm_file *file) >> Calling virtio_gpu_deinit() from virtio_gpu_release() might be a better >> option > > Wouldn't that end up freeing the virtqueues twice, or using them after > they are freed? virtio_gpu_deinit() would then run from both the > virtio_gpu_remove() path and the virtio_gpu_release() path. > or do you mean removing it from virtio_gpu_remove() and calling it only > from virtio_gpu_release()? > This is only from a high-level look so far. I'll look into it more > closely and get back to you. Remove from virtio_gpu_remove() and call only from virtio_gpu_release(). -- Best regards, Dmitry