Re: [PATCH 1/2] rcu: Fix casting while dereferencing rcu pointers

[David Laight <david.laight.linux@gmail.com>]

On Tue, 25 Aug 2026 20:02:10 +0000
Ricardo Ribalda <ribalda@chromium.org> wrote:

> Recent versions of smatch preserved the address space qualifiers with
> typeof()[1].
> 
> This fix has discovered an invalid casting in rcu dereference logic.
> 
> This patch fixes tens of smatch errors like the following:
> ./include/trace/events/vb2.h:46:1: warning: incorrect type in assignment (different address spaces)
> ./include/trace/events/vb2.h:46:1:    expected struct tracepoint_func *it_func_ptr
> ./include/trace/events/vb2.h:46:1:    got struct tracepoint_func __rcu *
> 
> [1] https://github.com/error27/smatch/commit/e53027a4e816a772403baafa83c09e4a94c1cb8f
> 
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  include/linux/rcupdate.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 44c07a66edff..80276cedda80 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -488,7 +488,7 @@ static __always_inline bool lockdep_assert_rcu_helper(bool c, const struct __ctx
>  context_unsafe(								\
>  	typeof(*p) *local = (typeof(*p) *__force)(p);			\
>  	rcu_check_sparse(p, __rcu);					\
> -	((typeof(*p) __force __kernel *)(local))			\
> +	((TYPEOF_UNQUAL(*p) __force __kernel *)(local))			\

Ugg... TYPEOF_UNQUAL() is absolutely horrid...
When __CHECKER__ is undefined the whole thing is just (p).

I suspect reducing all the definitions would measurably improve
kernel compile time (even before these changes).

David

>  )
>  /**
>   * unrcu_pointer - mark a pointer as not being RCU protected
> @@ -503,7 +503,7 @@ context_unsafe(								\
>  ({ \
>  	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
>  	rcu_check_sparse(p, space); \
> -	((typeof(*p) __force __kernel *)(local)); \
> +	((TYPEOF_UNQUAL(*p) __force __kernel *)(local)); \
>  }) )
>  #define __rcu_dereference_check(p, local, c, space) \
>  ({ \
> @@ -511,19 +511,19 @@ context_unsafe(								\
>  	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
>  	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
>  	rcu_check_sparse(p, space); \
> -	((typeof(*p) __force __kernel *)(local)); \
> +	((TYPEOF_UNQUAL(*p) __force __kernel *)(local)); \
>  })
>  #define __rcu_dereference_protected(p, local, c, space) \
>  ({ \
>  	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
>  	rcu_check_sparse(p, space); \
> -	((typeof(*p) __force __kernel *)(p)); \
> +	((TYPEOF_UNQUAL(*p) __force __kernel *)(p)); \
>  })
>  #define __rcu_dereference_raw(p, local) \
>  ({ \
>  	/* Dependency order vs. p above. */ \
>  	typeof(p) local = READ_ONCE(p); \
> -	((typeof(*p) __force __kernel *)(local)); \
> +	((TYPEOF_UNQUAL(*p) __force __kernel *)(local)); \
>  })
>  #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
>  
>