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

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Message-ID: <CACT4Y+bKqXknE--kTngznowLaY1b9h5oGWdWBR8w=nHv8F90AQ@mail.gmail.com>
Date:   Thu, 3 Jan 2019 10:04:49 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     syzbot <syzbot+6ea337c427f5083ebdf2@...kaller.appspotmail.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        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 Thu, Jan 3, 2019 at 9:55 AM Maarten Lankhorst
<maarten.lankhorst@...ux.intel.com> wrote:
>
> Op 30-12-2018 om 07:21 schreef syzbot:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    903b77c63167 Merge tag 'linux-kselftest-4.21-rc1' of git:/..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=12d0f553400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=53a2f2aa0b1f7606
> > dashboard link: https://syzkaller.appspot.com/bug?extid=6ea337c427f5083ebdf2
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120d906f400000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1024673b400000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+6ea337c427f5083ebdf2@...kaller.appspotmail.com
> >
> > RBP: 00007ffe369ca7a0 R08: 0000000000000001 R09: 00000000004009ce
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
> > R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
> >
> > ================================================
> > WARNING: lock held when returning to user space!
> > 4.20.0+ #174 Not tainted
> > ------------------------------------------------
> > syz-executor556/8153 is leaving the kernel with locks still held!
> > 1 lock held by syz-executor556/8153:
> >  #0: 000000005100c85c (crtc_ww_class_acquire){+.+.}, at: set_property_atomic+0xb3/0x330 drivers/gpu/drm/drm_mode_object.c:462
> >
> >
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@...glegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
>
> Just guessing..
>
> Does this help?

Hi Maarten,

Please either test or ask syzbot to test:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches

> -----
> diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
> index cd9bc0ce9be0..004191d01772 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) {
>
> --
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