5.10-stable review patch. If anyone has any objections, please let me know.
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From: Paul E. McKenney paulmck@kernel.org
[ Upstream commit 76c8eaafe4f061f3790112842a2fbb297e4bea88 ]
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 Stable-dep-of: 5f35a624c1e3 ("drm/nouveau/fence:: fix warning directly dereferencing a rcu pointer") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/rcupdate.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index ef8d56b18da6..8716a1706351 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -366,6 +366,20 @@ 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); \