linux-kernel - Re: [syzbot] inconsistent lock state in sync_info_debugfs

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Date:   Tue, 22 Nov 2022 20:48:05 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     syzbot <syzbot+007bfe0f3330f6e1e7d1@...kaller.appspotmail.com>
Cc:     bp@...en8.de, christian.koenig@....com,
        dri-devel@...ts.freedesktop.org, gustavo@...ovan.org,
        hdanton@...a.com, hpa@...or.com, jmattson@...gle.com,
        joro@...tes.org, kvm@...r.kernel.org,
        linaro-mm-sig-bounces@...ts.linaro.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, mark.rutland@....com,
        mingo@...hat.com, pbonzini@...hat.com, peterz@...radead.org,
        seanjc@...gle.com, sumit.semwal@...aro.org,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        vkuznets@...hat.com, wanpengli@...cent.com, will@...nel.org,
        x86@...nel.org
Subject: Re: [syzbot] inconsistent lock state in sync_info_debugfs_show

On Sun, 20 Nov 2022 at 21:51, syzbot
<syzbot+007bfe0f3330f6e1e7d1@...kaller.appspotmail.com> wrote:
>
> syzbot has bisected this issue to:
>
> commit 997acaf6b4b59c6a9c259740312a69ea549cc684
> Author: Mark Rutland <mark.rutland@....com>
> Date:   Mon Jan 11 15:37:07 2021 +0000
>
>     lockdep: report broken irq restoration

Ok this looks funny. I'm pretty sure the code in
drivers/dma-buf/sw_sync.c around sync_timeline_fence_lock is correct.
And we don't do anything that this patch claims to catch, it's all
just plain spin_lock_irq and spin_lock_irqsave usage. Only thing that
crossed my mind here is that maybe lockdep somehow ends up with two
different keys for the same spinlock? I'm really confused ...
-Daniel

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=115b350d880000
> start commit:   84368d882b96 Merge tag 'soc-fixes-6.1-3' of git://git.kern..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=135b350d880000
> console output: https://syzkaller.appspot.com/x/log.txt?x=155b350d880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6f4e5e9899396248
> dashboard link: https://syzkaller.appspot.com/bug?extid=007bfe0f3330f6e1e7d1
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=164376f9880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16cf0965880000
>
> Reported-by: syzbot+007bfe0f3330f6e1e7d1@...kaller.appspotmail.com
> Fixes: 997acaf6b4b5 ("lockdep: report broken irq restoration")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch