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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 1 Feb 2021 19:09:51 +0100
Message-ID: <CACT4Y+ZEPG0keEM5BzeqxnqOETyjPsa+7_cvGk=VDH+ErhyF-Q@mail.gmail.com>
Subject: Re: corrupted pvqspinlock in htab_map_update_elem
To:     Waiman Long <longman@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>, andrii@kernel.org,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>, kpsingh@kernel.org,
        netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>
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On Mon, Feb 1, 2021 at 6:54 PM Waiman Long <longman@redhat.com> wrote:
>
> On 2/1/21 6:23 AM, Peter Zijlstra wrote:
> > On Mon, Feb 01, 2021 at 10:50:58AM +0100, Peter Zijlstra wrote:
> >
> >>>   queued_spin_unlock arch/x86/include/asm/qspinlock.h:56 [inline]
> >>>   lockdep_unlock+0x10e/0x290 kernel/locking/lockdep.c:124
> >>>   debug_locks_off_graph_unlock kernel/locking/lockdep.c:165 [inline]
> >>>   print_usage_bug kernel/locking/lockdep.c:3710 [inline]
> >> Ha, I think you hit a bug in lockdep.
> > Something like so I suppose.
> >
> > ---
> > Subject: locking/lockdep: Avoid unmatched unlock
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Mon Feb 1 11:55:38 CET 2021
> >
> > Commit f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI"
> > inversions") overlooked that print_usage_bug() releases the graph_lock
> > and called it without the graph lock held.
> >
> > Fixes: f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
> > Reported-by: Dmitry Vyukov <dvyukov@google.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >   kernel/locking/lockdep.c |    3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -3773,7 +3773,7 @@ static void
> >   print_usage_bug(struct task_struct *curr, struct held_lock *this,
> >               enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
> >   {
> > -     if (!debug_locks_off_graph_unlock() || debug_locks_silent)
> > +     if (!debug_locks_off() || debug_locks_silent)
> >               return;
> >
> >       pr_warn("\n");
> > @@ -3814,6 +3814,7 @@ valid_state(struct task_struct *curr, st
> >           enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
> >   {
> >       if (unlikely(hlock_class(this)->usage_mask & (1 << bad_bit))) {
> > +             graph_unlock()
> >               print_usage_bug(curr, this, bad_bit, new_bit);
> >               return 0;
> >       }
>
> I have also suspected doing unlock without a corresponding lock. This
> patch looks good to me.
>
> Acked-by: Waiman Long <longman@redhat.com>

Just so that it's not lost: there is still a bug related to bpf map lock, right?