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Subject: Re: corrupted pvqspinlock in htab_map_update_elem
To:     Peter Zijlstra <peterz@infradead.org>,
        Dmitry Vyukov <dvyukov@google.com>
Cc:     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>
 <YBfPAvBa8bbSU2nZ@hirez.programming.kicks-ass.net>
 <YBfkuyIfB1+VRxXP@hirez.programming.kicks-ass.net>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <5936f4a4-f150-e56e-f07d-1efee06eba16@redhat.com>
Date:   Mon, 1 Feb 2021 12:53:53 -0500
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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>

Cheers,
Longman