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authorPaul E. McKenney <paulmck@kernel.org>2021-04-21 14:30:54 -0700
committerPaul E. McKenney <paulmck@kernel.org>2021-05-13 09:13:23 -0700
commit76c8eaafe4f061f3790112842a2fbb297e4bea88 (patch)
tree3f6feabd24c2677e9cafd06406183f7ff11abd41 /include/linux/rcupdate.h
parent3d3a0d1b508dcc47e82b0e12cde6585bc088b0cc (diff)
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
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 <toke@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'include/linux/rcupdate.h')
-rw-r--r--include/linux/rcupdate.h14
1 files changed, 14 insertions, 0 deletions
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); \