Re: [PATCH v15 16/26] nfsd: add LOCALIO support

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2024-09-03 at 10:34 -0400, Chuck Lever wrote:
> On Sat, Aug 31, 2024 at 06:37:36PM -0400, Mike Snitzer wrote:
> > From: Weston Andros Adamson <dros@primarydata.com>
> > 
> > Add server support for bypassing NFS for localhost reads, writes, and
> > commits. This is only useful when both the client and server are
> > running on the same host.
> > 
> > If nfsd_open_local_fh() fails then the NFS client will both retry and
> > fallback to normal network-based read, write and commit operations if
> > localio is no longer supported.
> > 
> > Care is taken to ensure the same NFS security mechanisms are used
> > (authentication, etc) regardless of whether localio or regular NFS
> > access is used.  The auth_domain established as part of the traditional
> > NFS client access to the NFS server is also used for localio.  Store
> > auth_domain for localio in nfsd_uuid_t and transfer it to the client
> > if it is local to the server.
> > 
> > Relative to containers, localio gives the client access to the network
> > namespace the server has.  This is required to allow the client to
> > access the server's per-namespace nfsd_net struct.
> > 
> > This commit also introduces the use of NFSD's percpu_ref to interlock
> > nfsd_destroy_serv and nfsd_open_local_fh, to ensure nn->nfsd_serv is
> > not destroyed while in use by nfsd_open_local_fh and other LOCALIO
> > client code.
> > 
> > CONFIG_NFS_LOCALIO enables NFS server support for LOCALIO.
> > 
> > Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
> > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > Co-developed-by: Mike Snitzer <snitzer@kernel.org>
> > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > Co-developed-by: NeilBrown <neilb@suse.de>
> > Signed-off-by: NeilBrown <neilb@suse.de>
> > 
> > Not-Acked-by: Chuck Lever <chuck.lever@oracle.com>
> > Not-Reviewed-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/nfsd/Makefile           |   1 +
> >  fs/nfsd/filecache.c        |   2 +-
> >  fs/nfsd/localio.c          | 112 +++++++++++++++++++++++++++++++++++++
> >  fs/nfsd/netns.h            |   4 ++
> >  fs/nfsd/nfsctl.c           |  25 ++++++++-
> >  fs/nfsd/trace.h            |   3 +-
> >  fs/nfsd/vfs.h              |   2 +
> >  include/linux/nfslocalio.h |   8 +++
> >  8 files changed, 154 insertions(+), 3 deletions(-)
> >  create mode 100644 fs/nfsd/localio.c
> > 
> > diff --git a/fs/nfsd/Makefile b/fs/nfsd/Makefile
> > index b8736a82e57c..18cbd3fa7691 100644
> > --- a/fs/nfsd/Makefile
> > +++ b/fs/nfsd/Makefile
> > @@ -23,3 +23,4 @@ nfsd-$(CONFIG_NFSD_PNFS) += nfs4layouts.o
> >  nfsd-$(CONFIG_NFSD_BLOCKLAYOUT) += blocklayout.o blocklayoutxdr.o
> >  nfsd-$(CONFIG_NFSD_SCSILAYOUT) += blocklayout.o blocklayoutxdr.o
> >  nfsd-$(CONFIG_NFSD_FLEXFILELAYOUT) += flexfilelayout.o flexfilelayoutxdr.o
> > +nfsd-$(CONFIG_NFS_LOCALIO) += localio.o
> > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> > index 89ff380ec31e..348c1b97092e 100644
> > --- a/fs/nfsd/filecache.c
> > +++ b/fs/nfsd/filecache.c
> > @@ -52,7 +52,7 @@
> >  #define NFSD_FILE_CACHE_UP		     (0)
> >  
> >  /* We only care about NFSD_MAY_READ/WRITE for this cache */
> > -#define NFSD_FILE_MAY_MASK	(NFSD_MAY_READ|NFSD_MAY_WRITE)
> > +#define NFSD_FILE_MAY_MASK	(NFSD_MAY_READ|NFSD_MAY_WRITE|NFSD_MAY_LOCALIO)
> >  
> >  static DEFINE_PER_CPU(unsigned long, nfsd_file_cache_hits);
> >  static DEFINE_PER_CPU(unsigned long, nfsd_file_acquisitions);
> > diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c
> > new file mode 100644
> > index 000000000000..75df709c6903
> > --- /dev/null
> > +++ b/fs/nfsd/localio.c
> > @@ -0,0 +1,112 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * NFS server support for local clients to bypass network stack
> > + *
> > + * Copyright (C) 2014 Weston Andros Adamson <dros@primarydata.com>
> > + * Copyright (C) 2019 Trond Myklebust <trond.myklebust@hammerspace.com>
> > + * Copyright (C) 2024 Mike Snitzer <snitzer@hammerspace.com>
> > + * Copyright (C) 2024 NeilBrown <neilb@suse.de>
> > + */
> > +
> > +#include <linux/exportfs.h>
> > +#include <linux/sunrpc/svcauth.h>
> > +#include <linux/sunrpc/clnt.h>
> > +#include <linux/nfs.h>
> > +#include <linux/nfs_common.h>
> > +#include <linux/nfslocalio.h>
> > +#include <linux/string.h>
> > +
> > +#include "nfsd.h"
> > +#include "vfs.h"
> > +#include "netns.h"
> > +#include "filecache.h"
> > +
> > +static const struct nfsd_localio_operations nfsd_localio_ops = {
> > +	.nfsd_open_local_fh = nfsd_open_local_fh,
> > +	.nfsd_file_put_local = nfsd_file_put_local,
> > +	.nfsd_file_file = nfsd_file_file,
> > +};
> > +
> > +void nfsd_localio_ops_init(void)
> > +{
> > +	memcpy(&nfs_to, &nfsd_localio_ops, sizeof(nfsd_localio_ops));
> > +}
> 
> Same comment as Neil: this should surface a pointer to the
> localio_ops struct. Copying the whole set of function pointers is
> generally unnecessary.
> 
> 
> > +
> > +/**
> > + * nfsd_open_local_fh - lookup a local filehandle @nfs_fh and map to nfsd_file
> > + *
> > + * @uuid: nfs_uuid_t which provides the 'struct net' to get the proper nfsd_net
> > + *        and the 'struct auth_domain' required for LOCALIO access
> > + * @rpc_clnt: rpc_clnt that the client established, used for sockaddr and cred
> > + * @cred: cred that the client established
> > + * @nfs_fh: filehandle to lookup
> > + * @fmode: fmode_t to use for open
> > + *
> > + * This function maps a local fh to a path on a local filesystem.
> > + * This is useful when the nfs client has the local server mounted - it can
> > + * avoid all the NFS overhead with reads, writes and commits.
> > + *
> > + * On successful return, returned nfsd_file will have its nf_net member
> > + * set. Caller (NFS client) is responsible for calling nfsd_serv_put and
> > + * nfsd_file_put (via nfs_to.nfsd_file_put_local).
> > + */
> > +struct nfsd_file *
> > +nfsd_open_local_fh(nfs_uuid_t *uuid,
> > +		   struct rpc_clnt *rpc_clnt, const struct cred *cred,
> > +		   const struct nfs_fh *nfs_fh, const fmode_t fmode)
> > +	__must_hold(rcu)
> > +{
> > +	int mayflags = NFSD_MAY_LOCALIO;
> > +	struct nfsd_net *nn = NULL;
> > +	struct net *net;
> > +	struct svc_cred rq_cred;
> > +	struct svc_fh fh;
> > +	struct nfsd_file *localio;
> > +	__be32 beres;
> > +
> > +	if (nfs_fh->size > NFS4_FHSIZE)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	/*
> > +	 * Not running in nfsd context, so must safely get reference on nfsd_serv.
> > +	 * But the server may already be shutting down, if so disallow new localio.
> > +	 * uuid->net is NOT a counted reference, but caller's rcu_read_lock() ensures
> > +	 * that if uuid->net is not NULL, then calling nfsd_serv_try_get() is safe
> > +	 * and if it succeeds we will have an implied reference to the net.
> > +	 */
> > +	net = rcu_dereference(uuid->net);
> > +	if (net)
> > +		nn = net_generic(net, nfsd_net_id);
> > +	if (unlikely(!nn || !nfsd_serv_try_get(nn)))
> > +		return ERR_PTR(-ENXIO);
> > +
> > +	/* Drop the rcu lock for nfsd_file_acquire_local() */
> > +	rcu_read_unlock();
> 
> I'm struggling with the locking logistics. Caller takes the RCU read
> lock, this function drops the lock, then takes it again. So:
> 
>  - A caller might rely on the lock being held continuously, but
>  - The API contract documented above doesn't indicate that this
>    function drops that lock
>  - The __must_hold(rcu) annotation doesn't indicate that this
>    function drops that lock, IIUC
> 
> Dropping and retaking the lock in here is an anti-pattern that
> should be avoided. I suggest we are better off in the long run if
> the caller does not need to take the RCU read lock, but instead,
> nfsd_open_local_fh takes it right here just for the rcu_dereference.
> 
> OTOH, Why drop the lock before calling nfsd_file_acquire_local()?
> The RCU read lock can safely be taken more than once in succession.
> 
> Let's rethink the locking strategy.
> 


Agreed. The only caller does this:

        rcu_read_lock();
        if (!rcu_access_pointer(uuid->net)) {
                rcu_read_unlock();
                return ERR_PTR(-ENXIO);
        }
        localio = nfs_to.nfsd_open_local_fh(uuid, rpc_clnt, cred,
                                            nfs_fh, fmode);
        rcu_read_unlock();

Maybe just move the check for uuid->net down into nfsd_open_local_fh,
and it can acquire the rcu_read_lock for itself?

> 
> > +
> > +	/* nfs_fh -> svc_fh */
> > +	fh_init(&fh, NFS4_FHSIZE);
> > +	fh.fh_handle.fh_size = nfs_fh->size;
> > +	memcpy(fh.fh_handle.fh_raw, nfs_fh->data, nfs_fh->size);
> > +
> > +	if (fmode & FMODE_READ)
> > +		mayflags |= NFSD_MAY_READ;
> > +	if (fmode & FMODE_WRITE)
> > +		mayflags |= NFSD_MAY_WRITE;
> > +
> > +	svcauth_map_clnt_to_svc_cred_local(rpc_clnt, cred, &rq_cred);
> > +
> > +	beres = nfsd_file_acquire_local(uuid->net, &rq_cred, uuid->dom,
> > +					&fh, mayflags, &localio);
> > +	if (beres) {
> > +		localio = ERR_PTR(nfs_stat_to_errno(be32_to_cpu(beres)));
> > +		nfsd_serv_put(nn);
> > +	}
> > +
> > +	fh_put(&fh);
> > +	if (rq_cred.cr_group_info)
> > +		put_group_info(rq_cred.cr_group_info);
> > +
> > +	rcu_read_lock();
> > +	return localio;
> > +}
> > +EXPORT_SYMBOL_GPL(nfsd_open_local_fh);
> > diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> > index e2d953f21dde..0fd31188a951 100644
> > --- a/fs/nfsd/netns.h
> > +++ b/fs/nfsd/netns.h
> > @@ -216,6 +216,10 @@ struct nfsd_net {
> >  	/* last time an admin-revoke happened for NFSv4.0 */
> >  	time64_t		nfs40_last_revoke;
> >  
> > +#if IS_ENABLED(CONFIG_NFS_LOCALIO)
> > +	/* Local clients to be invalidated when net is shut down */
> > +	struct list_head	local_clients;
> > +#endif
> >  };
> >  
> >  /* Simple check to find out if a given net was properly initialized */
> > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > index 64c1b4d649bc..3adbc05ebaac 100644
> > --- a/fs/nfsd/nfsctl.c
> > +++ b/fs/nfsd/nfsctl.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/sunrpc/svc.h>
> >  #include <linux/module.h>
> >  #include <linux/fsnotify.h>
> > +#include <linux/nfslocalio.h>
> >  
> >  #include "idmap.h"
> >  #include "nfsd.h"
> > @@ -2257,7 +2258,9 @@ static __net_init int nfsd_net_init(struct net *net)
> >  	get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
> >  	seqlock_init(&nn->writeverf_lock);
> >  	nfsd_proc_stat_init(net);
> > -
> > +#if IS_ENABLED(CONFIG_NFS_LOCALIO)
> > +	INIT_LIST_HEAD(&nn->local_clients);
> > +#endif
> >  	return 0;
> >  
> >  out_repcache_error:
> > @@ -2268,6 +2271,22 @@ static __net_init int nfsd_net_init(struct net *net)
> >  	return retval;
> >  }
> >  
> > +#if IS_ENABLED(CONFIG_NFS_LOCALIO)
> > +/**
> > + * nfsd_net_pre_exit - Disconnect localio clients from net namespace
> > + * @net: a network namespace that is about to be destroyed
> > + *
> > + * This invalidated ->net pointers held by localio clients
> > + * while they can still safely access nn->counter.
> > + */
> > +static __net_exit void nfsd_net_pre_exit(struct net *net)
> > +{
> > +	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> > +
> > +	nfs_uuid_invalidate_clients(&nn->local_clients);
> > +}
> > +#endif
> > +
> >  /**
> >   * nfsd_net_exit - Release the nfsd_net portion of a net namespace
> >   * @net: a network namespace that is about to be destroyed
> > @@ -2285,6 +2304,9 @@ static __net_exit void nfsd_net_exit(struct net *net)
> >  
> >  static struct pernet_operations nfsd_net_ops = {
> >  	.init = nfsd_net_init,
> > +#if IS_ENABLED(CONFIG_NFS_LOCALIO)
> > +	.pre_exit = nfsd_net_pre_exit,
> > +#endif
> >  	.exit = nfsd_net_exit,
> >  	.id   = &nfsd_net_id,
> >  	.size = sizeof(struct nfsd_net),
> > @@ -2322,6 +2344,7 @@ static int __init init_nfsd(void)
> >  	retval = genl_register_family(&nfsd_nl_family);
> >  	if (retval)
> >  		goto out_free_all;
> > +	nfsd_localio_ops_init();
> >  
> >  	return 0;
> >  out_free_all:
> > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > index d22027e23761..82bcefcd1f21 100644
> > --- a/fs/nfsd/trace.h
> > +++ b/fs/nfsd/trace.h
> > @@ -86,7 +86,8 @@ DEFINE_NFSD_XDR_ERR_EVENT(cant_encode);
> >  		{ NFSD_MAY_NOT_BREAK_LEASE,	"NOT_BREAK_LEASE" },	\
> >  		{ NFSD_MAY_BYPASS_GSS,		"BYPASS_GSS" },		\
> >  		{ NFSD_MAY_READ_IF_EXEC,	"READ_IF_EXEC" },	\
> > -		{ NFSD_MAY_64BIT_COOKIE,	"64BIT_COOKIE" })
> > +		{ NFSD_MAY_64BIT_COOKIE,	"64BIT_COOKIE" },	\
> > +		{ NFSD_MAY_LOCALIO,		"LOCALIO" })
> >  
> >  TRACE_EVENT(nfsd_compound,
> >  	TP_PROTO(
> > diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> > index 01947561d375..3ff146522556 100644
> > --- a/fs/nfsd/vfs.h
> > +++ b/fs/nfsd/vfs.h
> > @@ -33,6 +33,8 @@
> >  
> >  #define NFSD_MAY_64BIT_COOKIE		0x1000 /* 64 bit readdir cookies for >= NFSv3 */
> >  
> > +#define NFSD_MAY_LOCALIO		0x2000 /* for tracing, reflects when localio used */
> > +
> >  #define NFSD_MAY_CREATE		(NFSD_MAY_EXEC|NFSD_MAY_WRITE)
> >  #define NFSD_MAY_REMOVE		(NFSD_MAY_EXEC|NFSD_MAY_WRITE|NFSD_MAY_TRUNC)
> >  
> > diff --git a/include/linux/nfslocalio.h b/include/linux/nfslocalio.h
> > index 62419c4bc8f1..61f2c781dd50 100644
> > --- a/include/linux/nfslocalio.h
> > +++ b/include/linux/nfslocalio.h
> > @@ -6,6 +6,8 @@
> >  #ifndef __LINUX_NFSLOCALIO_H
> >  #define __LINUX_NFSLOCALIO_H
> >  
> > +#if IS_ENABLED(CONFIG_NFS_LOCALIO)
> > +
> >  #include <linux/module.h>
> >  #include <linux/list.h>
> >  #include <linux/uuid.h>
> > @@ -63,4 +65,10 @@ struct nfsd_localio_operations {
> >  extern void nfsd_localio_ops_init(void);
> >  extern struct nfsd_localio_operations nfs_to;
> >  
> > +#else   /* CONFIG_NFS_LOCALIO */
> > +static inline void nfsd_localio_ops_init(void)
> > +{
> > +}
> > +#endif  /* CONFIG_NFS_LOCALIO */
> > +
> >  #endif  /* __LINUX_NFSLOCALIO_H */
> > -- 
> > 2.44.0
> > 
> 

-- 
Jeff Layton <jlayton@kernel.org>