From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2B1ED106F2EA for ; Thu, 26 Mar 2026 08:22:36 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id DEB3610E1EA; Thu, 26 Mar 2026 08:22:35 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=lankhorst.se header.i=@lankhorst.se header.b="ZT8L9swP"; dkim-atps=neutral Received: from lankhorst.se (unknown [141.105.120.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6019610E1EA; Thu, 26 Mar 2026 08:22:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lankhorst.se; s=default; t=1774513350; bh=DP+xLY/0cjszNHvW273UfD/Tj4f7qCLjI945LY987Jo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZT8L9swP9xlPtxCVgNOwvYL7oUX12wznZFRVWU6oljYvO8OW1JFh7OoZdZH43fyBH 4az51fC8Ej+qKgFRrHeIiIXs61mICBStuXyVAuLw+0g269k02I+VkOF0iNcRkamh/8 2iT6nTU5S2BkWTQyKnMd/+34sL/oia0TlxJNeXK9Z+HPXYqaxGkTCiW8KJH3sIfTDJ zUyJNXWLXRv6TpX0bvI77VVkIpYXx86zeJAwMj0BjXEFLZzxdrLfg1JE/cstejNv6k UE3Dar3+vQ7O3qyfxv/Lwr8CdfP09E7M6niHNdynW6wgQPDj0Me6LRjwgBq/UEl4SY Co6SafjtY4fQA== From: Maarten Lankhorst To: dri-devel@lists.freedesktop.org Cc: intel-xe@lists.freedesktop.org, Maarten Lankhorst , =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= , Guenter Roeck , Simona Vetter Subject: [PATCH] Revert "drm: Fix use-after-free on framebuffers and property blobs when calling drm_dev_unplug" Date: Thu, 26 Mar 2026 09:22:18 +0100 Message-ID: <20260326082217.39941-2-dev@lankhorst.se> X-Mailer: git-send-email 2.51.0 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-xe-bounces@lists.freedesktop.org Sender: "Intel-xe" This reverts commit 6bee098b91417654703e17eb5c1822c6dfd0c01d. Den 2026-03-25 kl. 22:11, skrev Simona Vetter: > On Wed, Mar 25, 2026 at 10:26:40AM -0700, Guenter Roeck wrote: >> Hi, >> >> On Fri, Mar 13, 2026 at 04:17:27PM +0100, Maarten Lankhorst wrote: >>> When trying to do a rather aggressive test of igt's "xe_module_load >>> --r reload" with a full desktop environment and game running I noticed >>> a few OOPSes when dereferencing freed pointers, related to >>> framebuffers and property blobs after the compositor exits. >>> >>> Solve this by guarding the freeing in drm_file with drm_dev_enter/exit, >>> and immediately put the references from struct drm_file objects during >>> drm_dev_unplug(). >>> >> >> With this patch in v6.18.20, I get the warning backtraces below. >> The backtraces are gone with the patch reverted. > > Yeah, this needs to be reverted, reasoning below. Maarten, can you please > take care of that and feed the revert through the usual channels? I don't > think it's critical enough that we need to fast-track this into drm.git > directly. > > Quoting the patch here again: > >> drivers/gpu/drm/drm_file.c | 5 ++++- >> drivers/gpu/drm/drm_mode_config.c | 9 ++++++--- >> 2 files changed, 10 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c >> index ec820686b3021..f52141f842a1f 100644 >> --- a/drivers/gpu/drm/drm_file.c >> +++ b/drivers/gpu/drm/drm_file.c >> @@ -233,6 +233,7 @@ static void drm_events_release(struct drm_file *file_priv) >> void drm_file_free(struct drm_file *file) >> { >> struct drm_device *dev; >> + int idx; >> >> if (!file) >> return; >> @@ -249,9 +250,11 @@ void drm_file_free(struct drm_file *file) >> >> drm_events_release(file); >> >> - if (drm_core_check_feature(dev, DRIVER_MODESET)) { >> + if (drm_core_check_feature(dev, DRIVER_MODESET) && >> + drm_dev_enter(dev, &idx)) { > > This is misplaced for two reasons: > > - Even if we'd want to guarantee that we hold a drm_dev_enter/exit > reference during framebuffer teardown, we'd need to do this > _consistently over all callsites. Not ad-hoc in just one place that a > testcase hits. This also means kerneldoc updates of the relevant hooks > and at least a bunch of acks from other driver people to document the > consensus. > > - More importantly, this is driver responsibilities in general unless we > have extremely good reasons to the contrary. Which means this must be > placed in xe. > >> drm_fb_release(file); >> drm_property_destroy_user_blobs(dev, file); >> + drm_dev_exit(idx); >> } >> >> if (drm_core_check_feature(dev, DRIVER_SYNCOBJ)) >> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c >> index 84ae8a23a3678..e349418978f79 100644 >> --- a/drivers/gpu/drm/drm_mode_config.c >> +++ b/drivers/gpu/drm/drm_mode_config.c >> @@ -583,10 +583,13 @@ void drm_mode_config_cleanup(struct drm_device *dev) >> */ >> WARN_ON(!list_empty(&dev->mode_config.fb_list)); >> list_for_each_entry_safe(fb, fbt, &dev->mode_config.fb_list, head) { >> - struct drm_printer p = drm_dbg_printer(dev, DRM_UT_KMS, "[leaked fb]"); >> + if (list_empty(&fb->filp_head) || drm_framebuffer_read_refcount(fb) > 1) { >> + struct drm_printer p = drm_dbg_printer(dev, DRM_UT_KMS, "[leaked fb]"); > > This is also wrong: > > - Firstly, it's a completely independent bug, we do not smash two bugfixes > into one patch. > > - Secondly, it's again a driver bug: drm_mode_cleanup must be called when > the last drm_device reference disappears (hence the existence of > drmm_mode_config_init), not when the driver gets unbound. The fact that > this shows up in a callchain from a devres cleanup means the intel > driver gets this wrong (like almost everyone else because historically > we didn't know better). > > If we don't follow this rule, then we get races with this code here > running concurrently with drm_file fb cleanups, which just does not > work. Review pointed that out, but then shrugged it off with a confused > explanation: > > https://lore.kernel.org/all/e61e64c796ccfb17ae673331a3df4b877bf42d82.camel@linux.intel.com/ > > Yes this also means a lot of the other drm_device teardown that drivers > do happens way too early. There is a massive can of worms here of a > magnitude that most likely is much, much bigger than what you can > backport to stable kernels. Hotunplug is _hard_. Back to the drawing board, and fixing it in the intel display driver instead. Cc: Thomas Hellström Reported-by: Guenter Roeck Acked-by: Simona Vetter Signed-off-by: Maarten Lankhorst Fixes: 6bee098b9141 ("drm: Fix use-after-free on framebuffers and property blobs when calling drm_dev_unplug") --- drivers/gpu/drm/drm_file.c | 5 +---- drivers/gpu/drm/drm_mode_config.c | 9 +++------ 2 files changed, 4 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c index f52141f842a1f..ec820686b3021 100644 --- a/drivers/gpu/drm/drm_file.c +++ b/drivers/gpu/drm/drm_file.c @@ -233,7 +233,6 @@ static void drm_events_release(struct drm_file *file_priv) void drm_file_free(struct drm_file *file) { struct drm_device *dev; - int idx; if (!file) return; @@ -250,11 +249,9 @@ void drm_file_free(struct drm_file *file) drm_events_release(file); - if (drm_core_check_feature(dev, DRIVER_MODESET) && - drm_dev_enter(dev, &idx)) { + if (drm_core_check_feature(dev, DRIVER_MODESET)) { drm_fb_release(file); drm_property_destroy_user_blobs(dev, file); - drm_dev_exit(idx); } if (drm_core_check_feature(dev, DRIVER_SYNCOBJ)) diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c index 802bc4608abf5..d12db9b0bab81 100644 --- a/drivers/gpu/drm/drm_mode_config.c +++ b/drivers/gpu/drm/drm_mode_config.c @@ -577,13 +577,10 @@ void drm_mode_config_cleanup(struct drm_device *dev) */ WARN_ON(!list_empty(&dev->mode_config.fb_list)); list_for_each_entry_safe(fb, fbt, &dev->mode_config.fb_list, head) { - if (list_empty(&fb->filp_head) || drm_framebuffer_read_refcount(fb) > 1) { - struct drm_printer p = drm_dbg_printer(dev, DRM_UT_KMS, "[leaked fb]"); + struct drm_printer p = drm_dbg_printer(dev, DRM_UT_KMS, "[leaked fb]"); - drm_printf(&p, "framebuffer[%u]:\n", fb->base.id); - drm_framebuffer_print_info(&p, 1, fb); - } - list_del_init(&fb->filp_head); + drm_printf(&p, "framebuffer[%u]:\n", fb->base.id); + drm_framebuffer_print_info(&p, 1, fb); drm_framebuffer_free(&fb->base.refcount); } -- 2.51.0