Re: [PATCH] rcu: replace _________p1 with __UNIQUE_ID(rcu)
From: Paul E. McKenney
Date: Mon Sep 13 2021 - 19:11:14 EST
On Mon, Sep 13, 2021 at 04:41:31AM +0800, Chun-Hung Tseng wrote:
> This commit replaced _________p1 with __UNIQUE_ID(rcu), which
> generates unique variable names during compilation. Necessary
> modifications due to the changes in the RCU macros have also been
> reflected in this commit.
>
> The same idea is used for the min/max macros (commit 589a978 and commit
> e9092d0), which aims to reduce variable shadowing issues caused by hard
> coded variable names.
>
> Signed-off-by: Jim Huang <jserv@xxxxxxxxxxxxxxxx>
> Signed-off-by: Chun-Hung Tseng <henrybear327@xxxxxxxxx>
OK, I will bite...
> ---
> include/linux/rcupdate.h | 44 +++++++++++++++++++++++-----------------
> include/linux/srcu.h | 3 ++-
> 2 files changed, 27 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 434d12fe2d4f..a5ab20822040 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -370,39 +370,41 @@ static inline void rcu_preempt_sleep_check(void) { }
> * Converts @p from an __rcu pointer to a __kernel pointer.
> * This allows an __rcu pointer to be used with xchg() and friends.
> */
> -#define unrcu_pointer(p) \
> +#define __unrcu_pointer(p, local) \
> ({ \
> - typeof(*p) *_________p1 = (typeof(*p) *__force)(p); \
> + typeof(*p) *local = (typeof(*p) *__force)(p); \
Why not like this?
typeof(*p) *__UNIQUE_ID(rcu) = (typeof(*p) *__force)(p); \
Then we don't need the extra argument and the changes to the calls.
So what C-preprocessor subtlety am I missing?
Thanx, Paul
> rcu_check_sparse(p, __rcu); \
> - ((typeof(*p) __force __kernel *)(_________p1)); \
> + ((typeof(*p) __force __kernel *)(local)); \
> })
> +#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
>
> -#define __rcu_access_pointer(p, space) \
> +#define __rcu_access_pointer(p, local, space) \
> ({ \
> - typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
> + typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
> rcu_check_sparse(p, space); \
> - ((typeof(*p) __force __kernel *)(_________p1)); \
> + ((typeof(*p) __force __kernel *)(local)); \
> })
> -#define __rcu_dereference_check(p, c, space) \
> +#define __rcu_dereference_check(p, local, c, space) \
> ({ \
> /* Dependency order vs. p above. */ \
> - typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
> + 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 *)(________p1)); \
> + ((typeof(*p) __force __kernel *)(local)); \
> })
> -#define __rcu_dereference_protected(p, c, space) \
> +#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)); \
> })
> -#define rcu_dereference_raw(p) \
> +#define __rcu_dereference_raw(p, local) \
> ({ \
> /* Dependency order vs. p above. */ \
> - typeof(p) ________p1 = READ_ONCE(p); \
> - ((typeof(*p) __force __kernel *)(________p1)); \
> + typeof(p) local = READ_ONCE(p); \
> + ((typeof(*p) __force __kernel *)(local)); \
> })
> +#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
>
> /**
> * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
> @@ -489,7 +491,7 @@ do { \
> * when tearing down multi-linked structures after a grace period
> * has elapsed.
> */
> -#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
> +#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
>
> /**
> * rcu_dereference_check() - rcu_dereference with debug checking
> @@ -525,7 +527,8 @@ do { \
> * annotated as __rcu.
> */
> #define rcu_dereference_check(p, c) \
> - __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
> + __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
> + (c) || rcu_read_lock_held(), __rcu)
>
> /**
> * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
> @@ -540,7 +543,8 @@ do { \
> * rcu_read_lock() but also rcu_read_lock_bh() into account.
> */
> #define rcu_dereference_bh_check(p, c) \
> - __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
> + __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
> + (c) || rcu_read_lock_bh_held(), __rcu)
>
> /**
> * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
> @@ -555,7 +559,8 @@ do { \
> * only rcu_read_lock() but also rcu_read_lock_sched() into account.
> */
> #define rcu_dereference_sched_check(p, c) \
> - __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
> + __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
> + (c) || rcu_read_lock_sched_held(), \
> __rcu)
>
> /*
> @@ -565,7 +570,8 @@ do { \
> * The no-tracing version of rcu_dereference_raw() must not call
> * rcu_read_lock_held().
> */
> -#define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
> +#define rcu_dereference_raw_check(p) \
> + __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
>
> /**
> * rcu_dereference_protected() - fetch RCU pointer when updates prevented
> @@ -584,7 +590,7 @@ do { \
> * but very ugly failures.
> */
> #define rcu_dereference_protected(p, c) \
> - __rcu_dereference_protected((p), (c), __rcu)
> + __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
>
>
> /**
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index e6011a9975af..01226e4d960a 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -117,7 +117,8 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
> * lockdep_is_held() calls.
> */
> #define srcu_dereference_check(p, ssp, c) \
> - __rcu_dereference_check((p), (c) || srcu_read_lock_held(ssp), __rcu)
> + __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
> + (c) || srcu_read_lock_held(ssp), __rcu)
>
> /**
> * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
> --
> 2.25.1
>