From 76c8eaafe4f061f3790112842a2fbb297e4bea88 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 21 Apr 2021 14:30:54 -0700 Subject: rcu: Create an unrcu_pointer() to remove __rcu from a pointer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The xchg() and cmpxchg() functions are sometimes used to carry out RCU updates. Unfortunately, this can result in sparse warnings for both the old-value and new-value arguments, as well as for the return value. The arguments can be dealt with using RCU_INITIALIZER(): old_p = xchg(&p, RCU_INITIALIZER(new_p)); But a sparse warning still remains due to assigning the __rcu pointer returned from xchg to the (most likely) non-__rcu pointer old_p. This commit therefore provides an unrcu_pointer() macro that strips the __rcu. This macro can be used as follows: old_p = unrcu_pointer(xchg(&p, RCU_INITIALIZER(new_p))); Reported-by: Toke Høiland-Jørgensen Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 1199ffd305d1..b071d02a028a 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -363,6 +363,20 @@ static inline void rcu_preempt_sleep_check(void) { } #define rcu_check_sparse(p, space) #endif /* #else #ifdef __CHECKER__ */ +/** + * unrcu_pointer - mark a pointer as not being RCU protected + * @p: pointer needing to lose its __rcu property + * + * 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) \ +({ \ + typeof(*p) *_________p1 = (typeof(*p) *__force)(p); \ + rcu_check_sparse(p, __rcu); \ + ((typeof(*p) __force __kernel *)(_________p1)); \ +}) + #define __rcu_access_pointer(p, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \ -- cgit v1.2.3-58-ga151