On Thu, 2024-06-27 at 13:14 -0400, Mike Snitzer wrote: > On Thu, Jun 27, 2024 at 07:24:54AM -0400, Jeff Layton wrote: > > On Wed, 2024-06-26 at 14:24 -0400, Mike Snitzer wrote: > > > Introduce nfsd_serv_get and nfsd_serv_put and update the nfsd > > > code to > > > prevent nfsd_destroy_serv from destroying nn->nfsd_serv until any > > > client initiated localio calls to nfsd (that are _not_ in the > > > context > > > of nfsd) are complete. > > > > > > nfsd_open_local_fh is updated to nfsd_serv_get before opening its > > > file > > > handle and then drop the reference using nfsd_serv_put at the end > > > of > > > nfsd_open_local_fh. > > > > > > This "interlock" working relies heavily on nfsd_open_local_fh()'s > > > maybe_get_net() safely dealing with the possibility that the > > > struct > > > net (and nfsd_net by association) may have been destroyed by > > > nfsd_destroy_serv() via nfsd_shutdown_net(). > > > > > > Verified to fix an easy to hit crash that would occur if an nfsd > > > instance running in a container, with a localio client mounted, > > > is > > > shutdown. Upon restart of the container and associated nfsd the > > > client > > > would go on to crash due to NULL pointer dereference that > > > occuured due > > > to the nfs client's localio attempting to nfsd_open_local_fh(), > > > using > > > nn->nfsd_serv, without having a proper reference on nn- > > > >nfsd_serv. > > > > > > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> > > > --- > > > fs/nfsd/localio.c | 2 ++ > > > fs/nfsd/netns.h | 8 +++++++- > > > fs/nfsd/nfssvc.c | 39 +++++++++++++++++++++++++++++++++++++++ > > > 3 files changed, 48 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c > > > index 48118db801b5..819589ae2008 100644 > > > --- a/fs/nfsd/localio.c > > > +++ b/fs/nfsd/localio.c > > > @@ -204,6 +204,7 @@ int nfsd_open_local_fh(struct net *net, > > > } > > > nn = net_generic(net, nfsd_net_id); > > > > > > + nfsd_serv_get(nn); > > > serv = READ_ONCE(nn->nfsd_serv); > > > if (unlikely(!serv)) { > > > dprintk("%s: localio denied. Server not > > > running\n", __func__); > > > @@ -244,6 +245,7 @@ int nfsd_open_local_fh(struct net *net, > > > out_revertcred: > > > revert_creds(save_cred); > > > out_net: > > > + nfsd_serv_put(nn); > > > put_net(net); > > > return status; > > > } > > > diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h > > > index 0c5a1d97e4ac..17a73c780ca1 100644 > > > --- a/fs/nfsd/netns.h > > > +++ b/fs/nfsd/netns.h > > > @@ -13,6 +13,7 @@ > > > #include <linux/filelock.h> > > > #include <linux/nfs4.h> > > > #include <linux/percpu_counter.h> > > > +#include <linux/percpu-refcount.h> > > > #include <linux/siphash.h> > > > #include <linux/sunrpc/stats.h> > > > #include <linux/nfslocalio.h> > > > @@ -140,7 +141,9 @@ struct nfsd_net { > > > > > > struct svc_info nfsd_info; > > > #define nfsd_serv nfsd_info.serv > > > - > > > + struct percpu_ref nfsd_serv_ref; > > > + struct completion nfsd_serv_confirm_done; > > > + struct completion nfsd_serv_free_done; > > > > > > /* > > > * clientid and stateid data for construction of net > > > unique COPY > > > @@ -225,6 +228,9 @@ struct nfsd_net { > > > extern bool nfsd_support_version(int vers); > > > extern void nfsd_netns_free_versions(struct nfsd_net *nn); > > > > > > +void nfsd_serv_get(struct nfsd_net *nn); > > > +void nfsd_serv_put(struct nfsd_net *nn); > > > + > > > extern unsigned int nfsd_net_id; > > > > > > void nfsd_copy_write_verifier(__be32 verf[2], struct nfsd_net > > > *nn); > > > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c > > > index a477d2c5088a..be5acb7a4057 100644 > > > --- a/fs/nfsd/nfssvc.c > > > +++ b/fs/nfsd/nfssvc.c > > > @@ -258,6 +258,30 @@ int nfsd_minorversion(struct nfsd_net *nn, > > > u32 minorversion, enum vers_op change > > > return 0; > > > } > > > > > > +void nfsd_serv_get(struct nfsd_net *nn) > > > +{ > > > + percpu_ref_get(&nn->nfsd_serv_ref); > > > +} > > > + > > > +void nfsd_serv_put(struct nfsd_net *nn) > > > +{ > > > + percpu_ref_put(&nn->nfsd_serv_ref); > > > +} > > > + > > > +static void nfsd_serv_done(struct percpu_ref *ref) > > > +{ > > > + struct nfsd_net *nn = container_of(ref, struct nfsd_net, > > > nfsd_serv_ref); > > > + > > > + complete(&nn->nfsd_serv_confirm_done); > > > +} > > > + > > > +static void nfsd_serv_free(struct percpu_ref *ref) > > > +{ > > > + struct nfsd_net *nn = container_of(ref, struct nfsd_net, > > > nfsd_serv_ref); > > > + > > > + complete(&nn->nfsd_serv_free_done); > > > +} > > > + > > > /* > > > * Maximum number of nfsd processes > > > */ > > > @@ -462,6 +486,7 @@ static void nfsd_shutdown_net(struct net > > > *net) > > > lockd_down(net); > > > nn->lockd_up = false; > > > } > > > + percpu_ref_exit(&nn->nfsd_serv_ref); > > > #if IS_ENABLED(CONFIG_NFSD_LOCALIO) > > > list_del_rcu(&nn->nfsd_uuid.list); > > > #endif > > > @@ -544,6 +569,13 @@ void nfsd_destroy_serv(struct net *net) > > > struct nfsd_net *nn = net_generic(net, nfsd_net_id); > > > struct svc_serv *serv = nn->nfsd_serv; > > > > > > + lockdep_assert_held(&nfsd_mutex); > > > + > > > + percpu_ref_kill_and_confirm(&nn->nfsd_serv_ref, > > > nfsd_serv_done); > > > + wait_for_completion(&nn->nfsd_serv_confirm_done); > > > + wait_for_completion(&nn->nfsd_serv_free_done); > > > + /* percpu_ref_exit is called in nfsd_shutdown_net */ > > > + > > > > At this point where you're waiting on these completion vars, what > > stops > > the client from issuing new localio requests? > > The server going down. The interlock is with nfsd_open_local_fh, so > once any active file opens complete the server will get these > completions and the server will go down. The client will reconnect > if/when the server comes back up. > > Maybe I'm not imaginative enough, but is there risk of never-ending > overlapping file opens that prevent nfsd_destroy_serv() from > progressing? > Yeah, I think it's a possibility, especially if the underlying filesystem is particularly slow. You can probably solve that by just not handing out new references somehow once you're going to call percpu_ref_kill_and_confirm. -- Jeff Layton <jlayton@xxxxxxxxxx>