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

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Message-ID: <YCqbehyyeUoL0pPT@hirez.programming.kicks-ass.net>
Date:   Mon, 15 Feb 2021 17:04:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Shuah Khan <skhan@...uxfoundation.org>, 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, Feb 15, 2021 at 02:12:30PM +0100, Johannes Berg wrote:
> 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.

Correct, but I found it more symmetric vs the not implementation below.

> > -#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)?

Yeah, or frob a '*' in there.