Re: [PATCH 2/3] xfs: convert perag lookup to xarray

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Mon, Aug 12, 2024 at 04:39:56PM +0000, Pankaj Raghav (Samsung) wrote:
> On Mon, Aug 12, 2024 at 08:31:01AM +0200, Christoph Hellwig wrote:
> > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > index 7e80732cb54708..5efb1e8b4107a9 100644
> > --- a/fs/xfs/libxfs/xfs_ag.c
> > +++ b/fs/xfs/libxfs/xfs_ag.c
> > @@ -46,7 +46,7 @@ xfs_perag_get(
> >  	struct xfs_perag	*pag;
> >  
> >  	rcu_read_lock();
> xa_load() already calls rcu_read_lock(). So we can get rid of this I
> guess?

Almost certainly not; I assume pag is RCU-freed, so you'd be introducing
a UAF if the RCU lock is dropped before getting a refcount on the pag.