On Fri, 2023-01-06 at 10:05 +1100, NeilBrown wrote:
> On Thu, 05 Jan 2023, Jeff Layton wrote:
> > Even though there is a WARN_ON_ONCE check, it seems possible for
> > nfs4_find_file to race with the destruction of an fi_deleg_file while
> > trying to take a reference to it.
> >
> > put_deleg_file is done while holding the fi_lock. Take and hold it
> > when dealing with the fi_deleg_file in nfs4_find_file.
> >
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > fs/nfsd/nfs4state.c | 16 ++++++++++------
> > 1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index b68238024e49..3df3ae84bd07 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -6417,23 +6417,27 @@ nfsd4_lookup_stateid(struct nfsd4_compound_state *cstate,
> > static struct nfsd_file *
> > nfs4_find_file(struct nfs4_stid *s, int flags)
> > {
> > + struct nfsd_file *ret = NULL;
> > +
> > if (!s)
> > return NULL;
> >
> > switch (s->sc_type) {
> > case NFS4_DELEG_STID:
> > - if (WARN_ON_ONCE(!s->sc_file->fi_deleg_file))
> > - return NULL;
> > - return nfsd_file_get(s->sc_file->fi_deleg_file);
> > + spin_lock(&s->sc_file->fi_lock);
> > + if (!WARN_ON_ONCE(!s->sc_file->fi_deleg_file))
> > + ret = nfsd_file_get(s->sc_file->fi_deleg_file);
> > + spin_unlock(&s->sc_file->fi_lock);
> > + break;
>
> As an nfsd_file is freed with rcu, we don't need the spinlock.
>
> rcu_read_lock()
> ret = rcu_dereference(s->sc_file->fi_deleg_file);
> if (ret)
> ret = nfsd_file_get(ret);
> rcu_read_unlock();
>
> You could even put the NULL test in nfsd_file_get() and have:
>
> rcu_read_lock()l;
> ret = nfsd_file_get(rcu_dereference(s->sc_file->fi_deleg_file));
> rcu_read_unlock();
>
> but that might not be a win.
>
> I agree with Chuck that the WARNing isn't helpful.
>
>
Good point. I'll send a v2 set in a bit.
>
> > case NFS4_OPEN_STID:
> > case NFS4_LOCK_STID:
> > if (flags & RD_STATE)
> > - return find_readable_file(s->sc_file);
> > + ret = find_readable_file(s->sc_file);
> > else
> > - return find_writeable_file(s->sc_file);
> > + ret = find_writeable_file(s->sc_file);
> > }
> >
> > - return NULL;
> > + return ret;
> > }
> >
> > static __be32
> > --
> > 2.39.0
> >
> >
--
Jeff Layton <jlayton@xxxxxxxxxx>
