On Thu, Feb 06, 2025 at 04:42:51PM +1100, NeilBrown wrote:
> vfs_rmdir takes an exclusive lock on the target directory to ensure
> nothing new is created in it while the rmdir progresses. With the
> possibility of async updates continuing after the inode lock is dropped
> we now need extra protection.
>
> Any async updates will have DCACHE_PAR_UPDATE set on the dentry. We
> simply wait for that flag to be cleared on all children.
> +static void d_update_wait(struct dentry *dentry, unsigned int subclass)
> +{
> + /* Note this may only ever be called in a context where we have
> + * a lock preventing this dentry from becoming locked, possibly
> + * an update lock on the parent dentry. The must be a smp_mb()
> + * after that lock is taken and before this is called so that
> + * the following test is safe. d_update_lock() provides that
> + * barrier.
> + */
> + if (!(dentry->d_flags & DCACHE_PAR_UPDATE))
> + return
> + lock_acquire_exclusive(&dentry->d_update_map, subclass,
> + 0, NULL, _THIS_IP_);
What the fuck?
> + spin_lock(&dentry->d_lock);
> + wait_var_event_spinlock(&dentry->d_flags,
> + !check_dentry_locked(dentry),
> + &dentry->d_lock);
> + spin_unlock(&dentry->d_lock);
> + lock_map_release(&dentry->d_update_map);
> +}
OK, I realize that it compiles, but it should've raised all
kinds of red flags for anyone reading that. return + <newline> is
already fishy, but having the next line indented *less* than that
return is firmly in the "somebody's trying to hide something nasty
here" territory, even without parsing the damn thing.
