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 E17C23EF647; Wed, 20 May 2026 15:04:44 +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=1779289486; cv=pass; b=JRsizeU7YJw94HJt1TE9Rk69YVDHtUfdrHBeZNjoH1YNNFJZ7dLJ1VrehVJdqoqvCw37PitR+03hvilF18iI7dtyhEi6LH7n8sc/SyFdglY/bg4JJGejEopr4NwwIolmz3PBVl0rD5h0aF8JcTvAOhWuNcYkxz08CDpSQ6GakkQ= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779289486; c=relaxed/simple; bh=glHPaZzUi4OSH2qNpXzuKmnnplibFsR17/L3DDNefT4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=O4TygFb6JbOCf2My2HKjgTQFvJ40fn+FovIjAePXR15N3ZvU6/2oh4o5mJKPHn9kB7gIoeYdv3EiJiY1UnEbFlgUjyzH8D8ks2+5sMQIMyoRYY+HbZfZnPqHi+z3ZdU6gFYgBOmGZXmrUhbaG+scuCXJZU4fI+funs9ARB1mN2M= 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=dFcv12YC; 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="dFcv12YC" ARC-Seal: i=1; a=rsa-sha256; t=1779289462; cv=none; d=zohomail.com; s=zohoarc; b=H4H9wEPzL9F9DtuKYxJuHWRJCQZJ+AAQw8eTXUTgsdbgqWtPrLXuthO8YzeD7hBaiEIkya9PIMfxVfyKL4Wb03QL8904gzYW8epPtVniRJVqom0HlZ117Rmj+V7oOxuZc+FYgW5GzSJKQFfOXBLA1dktMobMc/9jIOUCO/7nSuU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1779289462; 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=aAAzUd7Ncpn7EM5gP2WjySDMAYuUVcl4Vo7wSz2utqs=; b=QNgx0gDg6ZY+o9niXoiW2GvJ7eGduzuJno2L/zBG95jaT8yIPmFS3Aj0cMu0y39yN9IgdGC+yLEgCmKrr+1ncQS58oFau0e6SxvOIMOO1IiSIvG3Ls4Z42sRcoXNC3q3eRrzWbjtLbhSEqS09p0hl4je0el9gC5P1AEixMT52Zg= 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=1779289462; 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=aAAzUd7Ncpn7EM5gP2WjySDMAYuUVcl4Vo7wSz2utqs=; b=dFcv12YC0WznA1JT+JNTOS5TAFX6vTuko9xjGSV+lXFs0GA2SxRRu7hj3KVE9qqj GuGFs78IcujNEp8CelYiL56dllabikrYRboVcEnFZ2WYppQlVWzO1NjQyrDDugJU2GG b+Dep1367e1TNtswNSddn/u0Fn08057sudkdzdTM= Received: by mx.zohomail.com with SMTPS id 1779289460798445.48512037796513; Wed, 20 May 2026 08:04:20 -0700 (PDT) Message-ID: <43ecdd2f-5faf-432a-a814-77190b3ef239@collabora.com> Date: Wed, 20 May 2026 18:04:14 +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: 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, christian.koenig@amd.com 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> Content-Language: en-US From: Dmitry Osipenko In-Reply-To: <20260519082247.34470-1-kartikey406@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ZohoMailClient: External On 5/19/26 11:22, 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. > > Both call sites run inside the .atomic_update plane callback, which > DRM atomic helpers do not allow to fail (by the time it runs, the > commit has been signed off to userspace and there is no clean > rollback path). Moving the lock acquisition to .prepare_fb was > rejected because the broader lock scope deadlocks against other BO > locking paths in the same atomic commit. > > Introduce virtio_gpu_lock_one_resv_uninterruptible() that uses > dma_resv_lock() instead of dma_resv_lock_interruptible(). This > eliminates the -EINTR failure mode -- the realistic syzbot trigger > -- without extending the lock hold across the commit. The helper > locks a single BO and rejects nents > 1 with -EINVAL; both fix > sites lock exactly one BO. > > Use it from virtio_gpu_cursor_plane_update() and > virtio_gpu_resource_flush(); check the return value to handle the > remaining -ENOMEM case from dma_resv_reserve_fences() by freeing > the objs and skipping the plane update for that frame. The > framebuffer BOs touched here are not shared with other contexts > and lock contention is expected to be brief, so the loss of > signal-interruptibility is acceptable. > > Other callers of virtio_gpu_array_lock_resv() (the ioctl paths) > continue to use the interruptible variant. > > The bug was reported by syzbot, triggered via fault injection > (fail_nth) on the DRM_IOCTL_MODE_CURSOR path, which forces the > -ENOMEM branch in dma_resv_reserve_fences(). > > Reported-by: syzbot+72bd3dd3a5d5f39a0271@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=72bd3dd3a5d5f39a0271 > Fixes: 5cfd31c5b3a3 ("drm/virtio: fix virtio_gpu_cursor_plane_update().") > Cc: stable@vger.kernel.org > Signed-off-by: Deepanshu Kartikey > --- > v4: Rename the helper to virtio_gpu_lock_one_resv_uninterruptible() > and reject objs->nents > 1 with -EINVAL. The v3 helper's > multi-object branch used drm_gem_lock_reservations(), which is > interruptible, contradicting the "uninterruptible" name; both > fix sites lock a single BO so the multi-object path is dropped. > (Dmitry Osipenko) > v3: Drop the prepare_fb/cleanup_fb approach from v2 (it deadlocked > against virtio_gpu_resource_flush(), which also locks the BO in > the same atomic commit). Instead add an uninterruptible variant > of the resv lock helper and use it in both > virtio_gpu_cursor_plane_update() and virtio_gpu_resource_flush(). > (Dmitry Osipenko) > v2: Move resv lock acquisition from .atomic_update (which must not > fail) to .prepare_fb (which may), per maintainer review of v1. > The v1 approach of silently skipping the cursor update on lock > failure violated the atomic-commit contract with userspace. > --- > drivers/gpu/drm/virtio/virtgpu_drv.h | 1 + > drivers/gpu/drm/virtio/virtgpu_gem.c | 17 +++++++++++++++++ > drivers/gpu/drm/virtio/virtgpu_plane.c | 10 ++++++++-- > 3 files changed, 26 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h > index f17660a71a3e..2f3531950aa4 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_drv.h > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h > @@ -317,6 +317,7 @@ virtio_gpu_array_from_handles(struct drm_file *drm_file, u32 *handles, u32 nents > void virtio_gpu_array_add_obj(struct virtio_gpu_object_array *objs, > struct drm_gem_object *obj); > int virtio_gpu_array_lock_resv(struct virtio_gpu_object_array *objs); > +int virtio_gpu_lock_one_resv_uninterruptible(struct virtio_gpu_object_array *objs); > void virtio_gpu_array_unlock_resv(struct virtio_gpu_object_array *objs); > void virtio_gpu_array_add_fence(struct virtio_gpu_object_array *objs, > struct dma_fence *fence); > diff --git a/drivers/gpu/drm/virtio/virtgpu_gem.c b/drivers/gpu/drm/virtio/virtgpu_gem.c > index f22dc5c21cd4..435d37d36034 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_gem.c > +++ b/drivers/gpu/drm/virtio/virtgpu_gem.c > @@ -238,6 +238,23 @@ int virtio_gpu_array_lock_resv(struct virtio_gpu_object_array *objs) > return ret; > } > > +int virtio_gpu_lock_one_resv_uninterruptible(struct virtio_gpu_object_array *objs) > +{ > + int ret; > + > + if (objs->nents != 1) > + return -EINVAL; > + > + dma_resv_lock(objs->objs[0]->resv, NULL); > + > + ret = dma_resv_reserve_fences(objs->objs[0]->resv, 1); > + if (ret) { > + virtio_gpu_array_unlock_resv(objs); > + return ret; > + } > + return 0; > +} > + > void virtio_gpu_array_unlock_resv(struct virtio_gpu_object_array *objs) > { > if (objs->nents == 1) { > diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c > index a126d1b25f46..652352424744 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_plane.c > +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c > @@ -215,7 +215,10 @@ static void virtio_gpu_resource_flush(struct drm_plane *plane, > if (!objs) > return; > virtio_gpu_array_add_obj(objs, vgfb->base.obj[0]); > - virtio_gpu_array_lock_resv(objs); > + if (virtio_gpu_lock_one_resv_uninterruptible(objs)) { > + virtio_gpu_array_put_free(objs); > + return; > + } > virtio_gpu_cmd_resource_flush(vgdev, bo->hw_res_handle, x, y, > width, height, objs, > vgplane_st->fence); > @@ -459,7 +462,10 @@ static void virtio_gpu_cursor_plane_update(struct drm_plane *plane, > if (!objs) > return; > virtio_gpu_array_add_obj(objs, vgfb->base.obj[0]); > - virtio_gpu_array_lock_resv(objs); > + if (virtio_gpu_lock_one_resv_uninterruptible(objs)) { > + virtio_gpu_array_put_free(objs); > + return; > + } > virtio_gpu_cmd_transfer_to_host_2d > (vgdev, 0, > plane->state->crtc_w, Applied to misc-next, thanks -- Best regards, Dmitry