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Subject: Re: corrupted pvqspinlock in htab_map_update_elem
To:     Dmitry Vyukov <dvyukov@google.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>
References: <CACT4Y+YJp0t0HA3+wDsAVxgTK4J+Pvht-J4-ENkOtS=C=Fhtzg@mail.gmail.com>
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 <5936f4a4-f150-e56e-f07d-1efee06eba16@redhat.com>
 <CACT4Y+ZEPG0keEM5BzeqxnqOETyjPsa+7_cvGk=VDH+ErhyF-Q@mail.gmail.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <19ca1c9f-090b-e97f-d9c7-827fa2f9fee5@redhat.com>
Date:   Mon, 1 Feb 2021 13:14:41 -0500
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On 2/1/21 1:09 PM, Dmitry Vyukov wrote:
> 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?
>
That is right. This patch just fixes the bug in lockdep.

Cheers,
Longman