On Thu, Aug 31, 2023 at 12:18:24PM +0200, Mateusz Guzik wrote:
> Turns out notify_change has the following:
> WARN_ON_ONCE(!inode_is_locked(inode));
>
> Which expands to:
> static inline int rwsem_is_locked(struct rw_semaphore *sem)
> {
> return atomic_long_read(&sem->count) != 0;
> }
>
> So it does check the lock, except it passes *any* locked state,
> including just readers.
>
> According to git blame this regressed from commit 5955102c9984
> ("wrappers for ->i_mutex access") by Al -- a bunch of mutex_is_locked
> were replaced with inode_is_locked, which unintentionally provides
> weaker guarantees.
>
> I don't see a rwsem helper for wlock check and I don't think it is all
> that beneficial to add. Instead, how about a bunch of lockdep, like so:
Yes, that's a good idea.
