linux-kernel - Re: [PATCH v5 07/36] lockdep: Annotate lockdep assertions for context analysis

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Message-ID: <cdde6c60-7f6f-4715-a249-5aab39438b57@acm.org>
Date: Fri, 19 Dec 2025 12:53:38 -0800
From: Bart Van Assche <bvanassche@....org>
To: Marco Elver <elver@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
 Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...nel.org>,
 Will Deacon <will@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
 Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
 Chris Li <sparse@...isli.org>, "Paul E. McKenney" <paulmck@...nel.org>,
 Alexander Potapenko <glider@...gle.com>, Arnd Bergmann <arnd@...db.de>,
 Christoph Hellwig <hch@....de>, Dmitry Vyukov <dvyukov@...gle.com>,
 Eric Dumazet <edumazet@...gle.com>, Frederic Weisbecker
 <frederic@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Herbert Xu <herbert@...dor.apana.org.au>, Ian Rogers <irogers@...gle.com>,
 Jann Horn <jannh@...gle.com>, Joel Fernandes <joelagnelf@...dia.com>,
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 <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
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Subject: Re: [PATCH v5 07/36] lockdep: Annotate lockdep assertions for context
 analysis

On 12/19/25 7:39 AM, Marco Elver wrote:
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index dd634103b014..621566345406 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)
>   
>   #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_lock(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_lock(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_lock(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_lock(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_lock(l)
> +#define lockdep_assert_held_read(l)		__assume_shared_ctx_lock(l)
>   #define lockdep_assert_held_once(l)		do { (void)(l); } while (0)
>   #define lockdep_assert_none_held_once()	do { } while (0)

I think these macros should use __must_hold() instead of __assume...().
lockdep_assert_held() emits a runtime warning if 'l' is not held. Hence,
I think that code where lockdep_assert_held() is used should not compile
if it cannot be verified at compile time that 'l' is held.

Thanks,

Bart.