[PATCH v3 1/3] rust: sync: Add abstraction for synchronize_rcu()

synchronize_rcu() is a frequently used C function which is always safe
to be called.

Add a safe abstraction for synchronize_rcu().

Signed-off-by: Philipp Stanner <[email protected]>
Reviewed-by: Onur Özkan <[email protected]>
Reviewed-by: Danilo Krummrich <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
---
 rust/kernel/sync/rcu.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/rust/kernel/sync/rcu.rs b/rust/kernel/sync/rcu.rs
index a32bef6e490b..2bae76d229f0 100644
--- a/rust/kernel/sync/rcu.rs
+++ b/rust/kernel/sync/rcu.rs
@@ -50,3 +50,19 @@ fn drop(&mut self) {
 pub fn read_lock() -> Guard {
     Guard::new()
 }
+
+/// Wait for one RCU grace period.
+///
+/// Waits for all RCU read-side critical sections (such as those established by
+/// a [`rcu::Guard`]) at the moment of the function call to finish.
+///
+/// Does not prevent new read-side critical sections from starting, which may
+/// begin and run while this call is blocking.
+///
+/// Note that this is one of the RCU primitives which must not be called in
+/// atomic context.
+#[inline]
+pub fn synchronize_rcu() {
+    // SAFETY: `synchronize_rcu()` is always safe to be called from process context.
+    unsafe { bindings::synchronize_rcu() };
+}
-- 
2.54.0