This is a note to let you know that I've just added the patch titled
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-create-an-unrcu_pointer-to-remove-__rcu-from-a-p.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7a28fd18ef02bc626536fc8a5d34e7fd479f39f5
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Thu Jun 24 18:05:51 2021 +0200
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
[ 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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Stable-dep-of: 5f35a624c1e3 ("drm/nouveau/fence:: fix warning directly dereferencing a rcu pointer")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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); \
