linux-kernel - Re: [PATCH v5 08/36] locking/rwlock, spinlock: Support Clang's context analysis

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Message-ID: <17723ae6-9611-4731-905c-60dab9fb7102@acm.org>
Date: Fri, 19 Dec 2025 12:26:16 -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>,
 Johannes Berg <johannes.berg@...el.com>, Jonathan Corbet <corbet@....net>,
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 <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
 Kentaro Takeda <takedakn@...data.co.jp>,
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 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
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 Steven Rostedt <rostedt@...dmis.org>,
 Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
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Subject: Re: [PATCH v5 08/36] locking/rwlock, spinlock: Support Clang's
 context analysis

On 12/19/25 7:39 AM, Marco Elver wrote:
> - extern void do_raw_read_lock(rwlock_t *lock) __acquires(lock);
> + extern void do_raw_read_lock(rwlock_t *lock) __acquires_shared(lock);

Given the "one change per patch" rule, shouldn't the annotation fixes
for rwlock operations be moved into a separate patch?

> -typedef struct {
> +context_lock_struct(rwlock) {
>   	arch_rwlock_t raw_lock;
>   #ifdef CONFIG_DEBUG_SPINLOCK
>   	unsigned int magic, owner_cpu;
> @@ -31,7 +31,8 @@ typedef struct {
>   #ifdef CONFIG_DEBUG_LOCK_ALLOC
>   	struct lockdep_map dep_map;
>   #endif
> -} rwlock_t;
> +};
> +typedef struct rwlock rwlock_t;

This change introduces a new globally visible "struct rwlock". Although
I haven't found any existing "struct rwlock" definitions, maybe it's a
good idea to use a more unique name instead.

> diff --git a/include/linux/spinlock_api_up.h b/include/linux/spinlock_api_up.h
> index 819aeba1c87e..018f5aabc1be 100644
> --- a/include/linux/spinlock_api_up.h
> +++ b/include/linux/spinlock_api_up.h
> @@ -24,68 +24,77 @@
>    * flags straight, to suppress compiler warnings of unused lock
>    * variables, and to add the proper checker annotations:
>    */
> -#define ___LOCK(lock) \
> -  do { __acquire(lock); (void)(lock); } while (0)
> +#define ___LOCK_void(lock) \
> +  do { (void)(lock); } while (0)

Instead of introducing a new macro ___LOCK_void(), please expand this
macro where it is used ((void)(lock)). I think this will make the code
in this header file easier to read.
    > -#define __LOCK(lock) \
> -  do { preempt_disable(); ___LOCK(lock); } while (0)
> +#define ___LOCK_(lock) \
> +  do { __acquire(lock); ___LOCK_void(lock); } while (0)

Is the macro ___LOCK_() used anywhere? If not, can it be left out?

> -#define __LOCK_BH(lock) \
> -  do { __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_LOCK_OFFSET); ___LOCK(lock); } while (0)
> +#define ___LOCK_shared(lock) \
> +  do { __acquire_shared(lock); ___LOCK_void(lock); } while (0)

The introduction of the new macros in this header file make the changes
hard to follow. Please consider splitting the changes for this header
file as follows:
* A first patch that splits ___LOCK() into ___LOCK_exclusive() and
   ___LOCK_shared().
* A second patch with the thread-safety annotation changes
   (__acquire() -> __acquire_shared()).

>   /* Non PREEMPT_RT kernels map spinlock to raw_spinlock */
> -typedef struct spinlock {
> +context_lock_struct(spinlock) {
>   	union {
>   		struct raw_spinlock rlock;
>   
> @@ -26,7 +26,8 @@ typedef struct spinlock {
>   		};
>   #endif
>   	};
> -} spinlock_t;
> +};
> +typedef struct spinlock spinlock_t;

Also here, a new global struct name is introduced (spinlock). Maybe the
name of this new struct should be made more unique?

Thanks,

Bart.