linux-kernel - Re: [PATCH v4 07/35] lockdep: Annotate lockdep assertions for context analysis

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Message-ID: <20251211114302.GC3911114@noisy.programming.kicks-ass.net>
Date: Thu, 11 Dec 2025 12:43:02 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Marco Elver <elver@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...nel.org>,
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Subject: Re: [PATCH v4 07/35] lockdep: Annotate lockdep assertions for
 context analysis

On Thu, Nov 20, 2025 at 04:09:32PM +0100, Marco Elver wrote:

>  include/linux/lockdep.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 67964dc4db95..2c99a6823161 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -282,16 +282,16 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
>  	do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0)

Since I typically read patches without first reading the Changelog --
because when I read the code later, I also don't see changelogs.

I must admit to getting most terribly confused here -- *again*, as I
then search back to previous discussions and found I was previously also
confused.

As such, I think we want a comment here that explains that assume_ctx
thing.

It is *NOT* (as the clang naming suggests) an assertion of holding the
lock (which is requires_ctx), but rather an annotation that forces the
ctx to be considered held.

>  
>  #define lockdep_assert_held(l)		\
> -	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
> +	do { lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD); __assume_ctx_guard(l); } while (0)
>  
>  #define lockdep_assert_not_held(l)	\
>  	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_HELD)
>  
>  #define lockdep_assert_held_write(l)	\
> -	lockdep_assert(lockdep_is_held_type(l, 0))
> +	do { lockdep_assert(lockdep_is_held_type(l, 0)); __assume_ctx_guard(l); } while (0)
>  
>  #define lockdep_assert_held_read(l)	\
> -	lockdep_assert(lockdep_is_held_type(l, 1))
> +	do { lockdep_assert(lockdep_is_held_type(l, 1)); __assume_shared_ctx_guard(l); } while (0)
>  
>  #define lockdep_assert_held_once(l)		\
>  	lockdep_assert_once(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
> @@ -389,10 +389,10 @@ extern int lockdep_is_held(const void *);
>  #define lockdep_assert(c)			do { } while (0)
>  #define lockdep_assert_once(c)			do { } while (0)
>  
> -#define lockdep_assert_held(l)			do { (void)(l); } while (0)
> +#define lockdep_assert_held(l)			__assume_ctx_guard(l)
>  #define lockdep_assert_not_held(l)		do { (void)(l); } while (0)
> -#define lockdep_assert_held_write(l)		do { (void)(l); } while (0)
> -#define lockdep_assert_held_read(l)		do { (void)(l); } while (0)
> +#define lockdep_assert_held_write(l)		__assume_ctx_guard(l)
> +#define lockdep_assert_held_read(l)		__assume_shared_ctx_guard(l)
>  #define lockdep_assert_held_once(l)		do { (void)(l); } while (0)
>  #define lockdep_assert_none_held_once()	do { } while (0)
>  
> -- 
> 2.52.0.rc1.455.g30608eb744-goog
>