From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-pp-f112.zoho.com (sender4-pp-f112.zoho.com [136.143.188.112]) (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 7B9913A759D; Wed, 20 May 2026 08:13:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.112 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779264820; cv=pass; b=EZjQk/tiNyqngCGL+RIBspC617y/sFAa9tr7g8EALVmLti0tXAGuszPyzRkSZ3LXxgy8iPSJF6tVsxUBafrhXOV1SPZO4v+ebn5LxyEunTDnQYHracG5WCGKO5MzVwklNOze68xlKbYguUy/6bdtY7/lZ/XFPQic21kLUrXawv8= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779264820; c=relaxed/simple; bh=UuHZN8bLdDb35hsZfOIbiCsj2GNcJv+JahtKBFao7JM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pKNMFiuXGETu7as/d6seWnmLSeRSihnDweFiyI7tHyzCU27PrsgyENEMvCJunHW3VgfA1rlTLfUwlAekOhmyHvSNJZL8cpE0R+/XScC+Uww/kHoEJcHN/LtalLretmo1n4ExjfxFxYO7GSDi0xYq3RXJI3krvBpT5Nxrfs15bRU= 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=Uh3wbPHC; arc=pass smtp.client-ip=136.143.188.112 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="Uh3wbPHC" ARC-Seal: i=1; a=rsa-sha256; t=1779264795; cv=none; d=zohomail.com; s=zohoarc; b=fhoFZAGE734g7YrwnK69+Fp+SlBP+e532/rwFxqqOg8FV5tdEIfaFORTiqM7n7YHad3es+GlWxlzsGHFrGKmdpYlnHvbmI07PynfxC0MmNg3KoTVLwV5hv//8Qm7A/9yCp5Bqp5lY06N0LRgOXEXr1Tm2J2d+40YejVZHso/9qc= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1779264795; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=1DaCzDhRImq3pbfy2r8JVXerCF/X/rQL52mfTWicG4k=; b=K3aH/+VmSSz2zNU3CCHPtj8w3HqysMSbIPKHzatggDefM46va4bIfeUqv9Yi8u7NpUttUonl5naq6Pn/swZE223u1Adj+zj2Zvh30+EWyGv6ZzG7yNetKASukVSTLQVsaovI58YmPid6/GP6ZYkLAv9PWmFKpTYTPnzTcqVhyL4= 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=1779264795; s=zohomail; d=collabora.com; i=dmitry.osipenko@collabora.com; h=Message-ID:Date:Date:MIME-Version:Subject:Subject:To:To:Cc:Cc:References:From:From:In-Reply-To:Content-Type:Content-Transfer-Encoding:Message-Id:Reply-To; bh=1DaCzDhRImq3pbfy2r8JVXerCF/X/rQL52mfTWicG4k=; b=Uh3wbPHCLetqao1sJ7Ww936T/0G+TEuQ9eZT1Mp+poKOwsOIjUnwdOOdRXAk4InP Uaty3nP1NfXa2mETMeGvPFJJqqvNUqPmcIWGCohU4EwEQ1nDdkykQdd/R7m2KjrSQ51 g2CJSVyOSfXMx1O01zyUaaPNsikI0NgfwcNfxCrI= Received: by mx.zohomail.com with SMTPS id 1779264793673372.72174741381184; Wed, 20 May 2026 01:13:13 -0700 (PDT) Message-ID: Date: Wed, 20 May 2026 11:12:53 +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 v4] drm/virtio: use uninterruptible resv lock for plane updates To: =?UTF-8?Q?Christian_K=C3=B6nig?= , Deepanshu Kartikey , airlied@redhat.com, kraxel@redhat.com, gurchetansingh@chromium.org, olvaffe@gmail.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, simona@ffwll.ch, sumit.semwal@linaro.org Cc: dri-devel@lists.freedesktop.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, syzbot+72bd3dd3a5d5f39a0271@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20260519082247.34470-1-kartikey406@gmail.com> <2e23513c-9d59-4891-acfe-9f1fbcbce778@amd.com> Content-Language: en-US From: Dmitry Osipenko In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External On 5/20/26 10:05, Christian König wrote: > On 5/20/26 08:50, Dmitry Osipenko wrote: >> On 5/19/26 11:27, Christian König wrote: >>> On 5/19/26 10:22, Deepanshu Kartikey wrote: >>>> virtio_gpu_cursor_plane_update() and virtio_gpu_resource_flush() lock >>>> the framebuffer BO's dma_resv via virtio_gpu_array_lock_resv() and >>>> ignore its return value. The function can fail with -EINTR from >>>> dma_resv_lock_interruptible() (signal during lock wait) or with >>>> -ENOMEM from dma_resv_reserve_fences() (fence slot allocation), >>>> leaving the resv lock not held. The queue path then walks the object >>>> array and calls dma_resv_add_fence(), which requires the lock held; >>>> with lockdep enabled this trips dma_resv_assert_held(): >>>> >>>> WARNING: drivers/dma-buf/dma-resv.c:296 at dma_resv_add_fence+0x71e/0x840 >>>> Call Trace: >>>> virtio_gpu_array_add_fence >>>> virtio_gpu_queue_ctrl_sgs >>>> virtio_gpu_queue_fenced_ctrl_buffer >>>> virtio_gpu_cursor_plane_update >>>> drm_atomic_helper_commit_planes >>>> drm_atomic_helper_commit_tail >>>> commit_tail >>>> drm_atomic_helper_commit >>>> drm_atomic_commit >>>> drm_atomic_helper_update_plane >>>> __setplane_atomic >>>> drm_mode_cursor_universal >>>> drm_mode_cursor_common >>>> drm_mode_cursor_ioctl >>>> drm_ioctl >>>> __x64_sys_ioctl >>>> >>>> Beyond the WARN, mutating the dma_resv fence list without the lock >>>> races with concurrent readers/writers and can corrupt the list. >>> >>> Well why are you trying to add a fence on an atomic mode set in the first place? >>> >>> That is usually an illegal operation here. >> That is pre-existing in the driver. It performs draw operation and in >> some cases waits for the completion during atomic. Whether all that >> syncing is correct is hard to say immediately as some of it may be >> historical edge cases. > > I'm not not so deeply in the atomic mode setting stuff but it strongly sounds like that this is seriously broken. > > The background is that the atomic mode set framework allows an output dma_fence which is signaled when the commit is finished. > > So when you allocate a fence slot and add a new fence to finish the atomic commit it is trivially possible that this cycles back and waits for the atomic commit to finish. In other words you have a deadlock. > > You probably need specially crafted userspace with the right timing to trigger that, but such issues are usually a rather big no-no and need to be fixed in the long term. > > Try to add dma_fence_begin_signaling() and dma_fence_end_signaling() annotation and enable lockdep, the tool should be able to point out if and what exactly goes wrong. > > The usual fix is to prepare everything before commit_tail is called (alloc memory, create, reserve slot, add dma_fence etc....) and then just send out the prepared commands later on. We tried with moving resv alloc to prepare_fb() in a previous patch version, it resulted in a non-trivial deadlocks. The goal of this patch is to fix immediate problem with a minimal code change. What you're saying is correct, but it may require a rather big refactoring of the code. In general, everything works okay today, so not really an urgent problem. -- Best regards, Dmitry