On Fri, Feb 07, 2025 at 09:06:58PM +0000, Al Viro wrote:
> 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.
Incidentally, that's where lockdep warnings you've mentioned are
coming from...
