netdev - Re: [PATCH 1/2] lockdep: add lockdep_assert_not

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Message-ID: <79aeb83a288051bd3a2a3f15e5ac42e06f154d48.camel@sipsolutions.net>
Date:   Mon, 15 Feb 2021 14:12:30 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Cc:     mingo@...hat.com, will@...nel.org, kvalo@...eaurora.org,
        davem@...emloft.net, kuba@...nel.org, ath10k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lockdep: add lockdep_assert_not_held()

On Mon, 2021-02-15 at 11:44 +0100, Peter Zijlstra wrote:
> 
> I think something like so will work, but please double check.

Yeah, that looks better.

> +++ b/include/linux/lockdep.h
> @@ -294,11 +294,15 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
>  
>  #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
>  
> -#define lockdep_assert_held(l)	do {				\
> -		WARN_ON(debug_locks && !lockdep_is_held(l));	\
> +#define lockdep_assert_held(l)	do {					\
> +		WARN_ON(debug_locks && lockdep_is_held(l) == 0));	\
>  	} while (0)

That doesn't really need to change? It's the same.

> -#define lockdep_assert_held_write(l)	do {			\
> +#define lockdep_assert_not_held(l)	do {				\
> +		WARN_ON(debug_locks && lockdep_is_held(l) == 1));	\
> +	} while (0)
> +
> +#define lockdep_assert_held_write(l)	do {				\
>  		WARN_ON(debug_locks && !lockdep_is_held_type(l, 0));	\
>  	} while (0)
>  
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index c1418b47f625..983ba206f7b2 100644
> --- a/kernel/locking/lockdep.
> +++ b/kernel/locking/lockdep.c
> @@ -5467,7 +5467,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
>  	int ret = 0;
>  
>  	if (unlikely(!lockdep_enabled()))
> -		return 1; /* avoid false negative lockdep_assert_held() */
> +		return -1; /* avoid false negative lockdep_assert_held() */

Maybe add lockdep_assert_not_held() to the comment, to explain the -1
(vs non-zero)?

johannes