linux-kernel - Re: WARNING: lock held when returning to user space in set_property

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Date:   Fri, 4 Jan 2019 19:04:11 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     syzbot <syzbot+6ea337c427f5083ebdf2@...kaller.appspotmail.com>,
        DRI <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, maxime.ripard@...tlin.com,
        sean@...rly.run, syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING: lock held when returning to user space in
 set_property_atomic

On 2019/01/03 18:04, Dmitry Vyukov wrote:
> On Thu, Jan 3, 2019 at 9:55 AM Maarten Lankhorst <maarten.lankhorst@...ux.intel.com> wrote:
>> Just guessing..
>>
>> Does this help?

Yes it will. And while at it, let's fix another one together.

>From 291e42211e3cc6d85c915772717dd08d40fb5fed Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Fri, 4 Jan 2019 15:23:47 +0900
Subject: [PATCH] gpu/drm: Fix lock held when returning to user space.

We need to call drm_modeset_acquire_fini() when drm_atomic_state_alloc()
failed or call drm_modeset_acquire_init() after drm_atomic_state_alloc()
succeeded.

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+6ea337c427f5083ebdf2@...kaller.appspotmail.com>
---
 drivers/gpu/drm/drm_atomic_uapi.c | 3 +--
 drivers/gpu/drm/drm_mode_object.c | 4 ++--
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index c408898..9a1f41a 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -1296,12 +1296,11 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 			(arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
 		return -EINVAL;
 
-	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
-
 	state = drm_atomic_state_alloc(dev);
 	if (!state)
 		return -ENOMEM;
 
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 	state->acquire_ctx = &ctx;
 	state->allow_modeset = !!(arg->flags & DRM_MODE_ATOMIC_ALLOW_MODESET);
 
diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
index cd9bc0c..004191d 100644
--- a/drivers/gpu/drm/drm_mode_object.c
+++ b/drivers/gpu/drm/drm_mode_object.c
@@ -459,11 +459,11 @@ static int set_property_atomic(struct drm_mode_object *obj,
 	struct drm_modeset_acquire_ctx ctx;
 	int ret;
 
-	drm_modeset_acquire_init(&ctx, 0);
-
 	state = drm_atomic_state_alloc(dev);
 	if (!state)
 		return -ENOMEM;
+
+	drm_modeset_acquire_init(&ctx, 0);
 	state->acquire_ctx = &ctx;
 retry:
 	if (prop == state->dev->mode_config.dpms_property) {
-- 
1.8.3.1