Subject: Re: [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) *

From: Mathieu Desnoyers <[email-masked]>
Date: Tue, 5 Oct 2021 11:15:12 -0400 (EDT)

----- On Oct 5, 2021, at 9:47 AM, rostedt [email-masked] wrote:
[...]
> #define rcu_dereference_raw(p) \
> ({ \
> 	/* Dependency order vs. p above. */ \
> 	typeof(p) ________p1 = READ_ONCE(p); \
> -	((typeof(*p) __force __kernel *)(________p1)); \
> +	((typeof(p) __force __kernel)(________p1)); \
> })

AFAIU doing so removes validation that @p is indeed a pointer, so a user might mistakenly
try to use rcu_dereference() on an integer, and get away with it. I'm not sure we want to
loosen this check. I wonder if there might be another way to achieve the same check without
requiring the structure to be declared, e.g. with __builtin_types_compatible_p ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com