Re: corrupted pvqspinlock in htab_map_update_elem

[Waiman Long <longman@redhat.com>]

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