rust: sync: Add lock::Backend::assert_is_held()

Since we've exposed Lock::from_raw() and Guard::new() publically, we
want to be able to make sure that we assert that a lock is actually held
when constructing a Guard for it to handle instances of unsafe
Guard::new() calls outside of our lock module.

Hence add a new method assert_is_held() to Backend, which uses lockdep
to check whether or not a lock has been acquired. When lockdep is
disabled, this has no overhead.

[Boqun: Resolve the conflicts with exposing Guard::new(), reword the
 commit log a bit and format "unsafe { <statement>; }" into "unsafe {
 <statement> }" for the consistency. ]

Signed-off-by: Lyude Paul <[email protected]>
Signed-off-by: Boqun Feng <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

1 files changed, 5 insertions, 0 deletions

diff --git a/rust/helpers/mutex.c b/rust/helpers/mutex.c
index 7e00680958ef..06575553eda5 100644
--- a/rust/helpers/mutex.c
+++ b/rust/helpers/mutex.c
@@ -12,3 +12,8 @@ void rust_helper___mutex_init(struct mutex *mutex, const char *name,
 {
 	__mutex_init(mutex, name, key);
 }
+
+void rust_helper_mutex_assert_is_held(struct mutex *mutex)
+{
+	lockdep_assert_held(mutex);
+}