From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 BBD0643C7C2; Thu, 30 Jul 2026 14:56:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785423391; cv=none; b=lGnVo1oKO6tTzVkf24vy332Aj3MTwS5whWToACwqlBvPRu5NoqoiHru9/BUeGBj21yf641yS3Xg83xrxTD37O4A3ipTOIL5Mr9Dw3+SACPEWriiI8dpyiGB4yHIbrgtlr8mJiZSrrgC7o11NzNTcCfs3iQD7tjk57xRErVqrJL8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785423391; c=relaxed/simple; bh=y8WyXDazt8em5RDur2RCW0x9TMx9wnOxAI/WqlvLxL0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NWKNKleh6VBuflx1P+R4HcOARdMHF9U8V30VhlsvHNsxqW9mXv5QpDh9lNoKhYH47iv+BBqJhu7Aj611LTwBXxqv30MiajHi4zmAPG04TAxoZxye1S924K4QW+3m+baVq4+mWQpJNmC9mO02/pRqTCENzzqHNHZkscY4mJiIH78= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Up9IOatj; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Up9IOatj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCEB11F000E9; Thu, 30 Jul 2026 14:56:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1785423390; bh=qbrV03dMxlc1XUIcyNO5m1bm0RCY5ziZGJdmgWUIIks=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Up9IOatjTIhXXsF2QeT2iqmbpbE8i/JSioFvjZXv2AF25MFuXC+/D3yMSoDlgxCds U3VgDrDP7YIwMy3dz6ss5V9vcWBx7OaD110Je2ixmWYm1cVJ6bznP5xIrZfnL0sfHv pE2pRsqYiPMPNLkJcABPCpvFXQzRx4tbfT3prWMU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Dmitry Osipenko , Ryosuke Yasuoka , Sasha Levin Subject: [PATCH 6.18 007/675] drm/virtio: fix deadlock in display_info_cb by removing hotplug from dequeue worker Date: Thu, 30 Jul 2026 16:05:37 +0200 Message-ID: <20260730141445.272563639@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260730141445.110192266@linuxfoundation.org> References: <20260730141445.110192266@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ryosuke Yasuoka [ Upstream commit d1b894c5bbb3fee0012bd14356286dc2384e8213 ] A probe-time deadlock can occur between the dequeue worker and drm_client_register(). During probe, drm_client_register() holds clientlist_mutex and calls the fbdev hotplug callback, which triggers an atomic commit that ends up sleeping in virtio_gpu_queue_ctrl_sgs() waiting for virtqueue space. The dequeue worker that would free that space calls virtio_gpu_cmd_get_display_info_cb(), which invokes drm_kms_helper_hotplug_event() -> drm_client_dev_hotplug(), attempting to acquire the same clientlist_mutex. Since wake_up() is only called after the resp_cb loop, the probe thread is never woken and both threads deadlock. Fix this by removing the hotplug notification from virtio_gpu_cmd_get_display_info_cb(). The display data (outputs[i].info) is still updated synchronously in the callback. For the init path, drm_client_register() already fires an initial hotplug when the client is registered, which picks up the connector state updated by display_info_cb. For the runtime config_changed path, add a wait_event_timeout() in config_changed_work_func() so that display_info_cb updates the connector data before the hotplug notification is sent. Also replace drm_helper_hpd_irq_event() with drm_kms_helper_hotplug_event() since virtio-gpu never calls drm_kms_helper_poll_init() and thus drm_helper_hpd_irq_event() always returns false without doing anything. Fixes: 27655b9bb9f0 ("drm/client: Send hotplug event after registering a client") Closes: https://syzkaller.appspot.com/bug?id=d6dd6f86d3aaf7eebe7406e45c1c6e549453f224 Closes: https://syzkaller.appspot.com/bug?id=908bd910da5dd79b88de4cf7baf376cc873a922e Suggested-by: Dmitry Osipenko Signed-off-by: Ryosuke Yasuoka Signed-off-by: Dmitry Osipenko Link: https://patch.msgid.link/20260713-virtiogpu_syzbot-v2-1-2958fa37d46d@redhat.com Signed-off-by: Sasha Levin --- drivers/gpu/drm/virtio/virtgpu_kms.c | 5 ++++- drivers/gpu/drm/virtio/virtgpu_vq.c | 3 --- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c index 1c15cbf326b78c..4a25347734fda4 100644 --- a/drivers/gpu/drm/virtio/virtgpu_kms.c +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c @@ -48,7 +48,10 @@ static void virtio_gpu_config_changed_work_func(struct work_struct *work) virtio_gpu_cmd_get_edids(vgdev); virtio_gpu_cmd_get_display_info(vgdev); virtio_gpu_notify(vgdev); - drm_helper_hpd_irq_event(vgdev->ddev); + wait_event_timeout(vgdev->resp_wq, + !vgdev->display_info_pending, + 5 * HZ); + drm_kms_helper_hotplug_event(vgdev->ddev); } events_clear |= VIRTIO_GPU_EVENT_DISPLAY; } diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c index 8181b22b9b46a1..412384e16daea4 100644 --- a/drivers/gpu/drm/virtio/virtgpu_vq.c +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c @@ -839,9 +839,6 @@ static void virtio_gpu_cmd_get_display_info_cb(struct virtio_gpu_device *vgdev, vgdev->display_info_pending = false; spin_unlock(&vgdev->display_info_lock); wake_up(&vgdev->resp_wq); - - if (!drm_helper_hpd_irq_event(vgdev->ddev)) - drm_kms_helper_hotplug_event(vgdev->ddev); } static void virtio_gpu_cmd_get_capset_info_cb(struct virtio_gpu_device *vgdev, -- 2.53.0