From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 287C7606A31A for ; Sat, 31 Oct 2026 23:18:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=I8b3M8Az Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6EC6910E09A; Sat, 31 Oct 2026 23:18:49 +0000 (UTC) Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 20CE910E09A for ; Sat, 31 Oct 2026 23:18:43 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id CAADC42AED; Sat, 31 Oct 2026 23:18:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E1D91F000C1; Sat, 31 Oct 2026 23:18:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793488722; bh=VZ6McD+kEVWLGGaG8Se7D2c8sljMtFQpOMHcBFYO0nY=; h=From:Subject:Reply-To:To:In-Reply-To:References:Date; b=I8b3M8Azmz6wzkUshoi47VsGyxdU8stTHlOeWMyvYi+OPFMkNsZF5NlSvDOx68qmC pSqEUKsFcnVsTv0cqEP60eOAh4rq09rU39Onk/LVshNkuFhbOZQMFwOsYNbSmffVuN X5WLVDSeKQU1YsNfHF4zsPwD0WuN8sJ9Y43T4tGWn+W8ox6j44xtr9/v18Dm3yc01J K58oRuGckk68oufYvaTt8IuGYnCDViK69KnkKenLTaPNNN3vYGNt+b+VYQS/uPH+hw l22Kyu5zTZBFOhRpjynAWtF9PjHNl6EKzQqCbT3ShCig37bT3jjrdf+AMVuv2zkgRh Z9+PeYpJyxbSw== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH 2/2] drm/vkms: Use drm_dev_unplug() for ConfigFS device removal To: "Sebastian Wick" , dri-devel@lists.freedesktop.org In-Reply-To: <20261031225901.3200167-2-sebastian.wick@redhat.com> References: <20261031225901.3200167-1-sebastian.wick@redhat.com> <20261031225901.3200167-2-sebastian.wick@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 31 Oct 2026 23:18:42 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Sender: "dri-devel" X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 X-Archived-By: Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: - [High] drm/vkms: broken CRC debugfs unplug handling in vkms_destroy() -- commit 58c6203197ea5aa86a82e01783503c18d44dd2a1 Author: Sebastian Wick drm/vkms: Use drm_dev_unplug() for ConfigFS device removal This commit switches vkms_destroy() from drm_dev_unregister() to drm_dev_unplug() so that ioctls on open file descriptors are rejected with -ENODEV and in-flight operations guarded by drm_dev_enter()/drm_dev_exit() complete before ConfigFS device removal proceeds. > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_= drv.c > index 5a640b531d88f..716f9c966c211 100644 > --- a/drivers/gpu/drm/vkms/vkms_drv.c > +++ b/drivers/gpu/drm/vkms/vkms_drv.c > @@ -259,7 +259,7 @@ void vkms_destroy(struct vkms_config *config) > =20 > fdev =3D config->dev->faux_dev; > =20 > - drm_dev_unregister(&config->dev->drm); > + drm_dev_unplug(&config->dev->drm); > drm_atomic_helper_shutdown(&config->dev->drm); > devres_release_group(&fdev->dev, NULL); [Severity: High] How does this interact with an open CRTC CRC debugfs file descriptor (/sys/kernel/debug/dri//crtc-/crc/data) when the VKMS device is disabled via ConfigFS? In drivers/gpu/drm/vkms/vkms_composer.c, vkms_set_crc_source() guards the callback with drm_dev_enter(): drivers/gpu/drm/vkms/vkms_composer.c:vkms_set_crc_source() { ... if (!drm_dev_enter(crtc->dev, &idx)) return -ENODEV; ret =3D vkms_crc_parse_source(src_name, &enabled); vkms_set_composer(out, enabled); drm_dev_exit(idx); return ret; } When the crc/data file descriptor is closed, full_proxy_release() invokes crtc_crc_release() in drivers/gpu/drm/drm_debugfs_crc.c, which calls crtc->funcs->set_crc_source(crtc, NULL). Two issues seem possible here: 1. Unlike /dev/dri/card file descriptors, opening crc/data via crtc_crc_open() does not acquire a drm_dev_get() reference on crtc->dev, and debugfs_remove_recursive() during drm_dev_unregister() does not wait for open file descriptors to close. In vkms_destroy(), drm_dev_unplug() runs synchronize_srcu() before devres_release_group(&fdev->dev, NULL) drops the devm reference via devm_drm_dev_init_release() -> drm_dev_put(). If no /dev/dri/card fd is open (or after it is closed first, such as during process exit when card has a lower fd number than crc/data), drm_dev_release() frees struct vkms_output (embedding struct drm_crtc) and struct vkms_device (embedding struct drm_device). When the crc/data fd is subsequently closed, wouldn't crtc_crc_release() and drm_dev_enter(crtc->dev, &idx) in vkms_set_crc_source() dereference the freed struct drm_crtc and crtc->dev? 2. Conversely, if struct drm_device is still kept alive by an open /dev/dri/card fd when crc/data is closed after drm_dev_unplug() sets dev->unplugged =3D true, drm_dev_enter(crtc->dev, &idx) in vkms_set_crc_source(crtc, NULL) will return false and exit early with -ENODEV. Doesn't that skip vkms_set_composer(out, false), leaving out->composer_enabled set to true and leaking the vblank reference from drm_crtc_vblank_put(&out->crtc)? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261031225901.3200= 167-1-sebastian.wick@redhat.com?part=3D2