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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, "J. Bruce Fields" <bfields@redhat.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.7 071/112] nfsd: clients dont need to break their own delegations
Date:   Tue,  7 Jul 2020 17:17:16 +0200
Message-Id: <20200707145804.379713164@linuxfoundation.org>
In-Reply-To: <20200707145800.925304888@linuxfoundation.org>
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From: J. Bruce Fields <bfields@redhat.com>

[ Upstream commit 28df3d1539de5090f7916f6fff03891b67f366f4 ]

We currently revoke read delegations on any write open or any operation
that modifies file data or metadata (including rename, link, and
unlink).  But if the delegation in question is the only read delegation
and is held by the client performing the operation, that's not really
necessary.

It's not always possible to prevent this in the NFSv4.0 case, because
there's not always a way to determine which client an NFSv4.0 delegation
came from.  (In theory we could try to guess this from the transport
layer, e.g., by assuming all traffic on a given TCP connection comes
from the same client.  But that's not really correct.)

In the NFSv4.1 case the session layer always tells us the client.

This patch should remove such self-conflicts in all cases where we can
reliably determine the client from the compound.

To do that we need to track "who" is performing a given (possibly
lease-breaking) file operation.  We're doing that by storing the
information in the svc_rqst and using kthread_data() to map the current
task back to a svc_rqst.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 Documentation/filesystems/locking.rst |  2 ++
 fs/locks.c                            |  3 +++
 fs/nfsd/nfs4proc.c                    |  2 ++
 fs/nfsd/nfs4state.c                   | 14 ++++++++++++++
 fs/nfsd/nfsd.h                        |  2 ++
 fs/nfsd/nfssvc.c                      |  6 ++++++
 include/linux/fs.h                    |  1 +
 include/linux/sunrpc/svc.h            |  1 +
 8 files changed, 31 insertions(+)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 5057e4d9dcd1d..9fdcec4166142 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -425,6 +425,7 @@ prototypes::
 	int (*lm_grant)(struct file_lock *, struct file_lock *, int);
 	void (*lm_break)(struct file_lock *); /* break_lease callback */
 	int (*lm_change)(struct file_lock **, int);
+	bool (*lm_breaker_owns_lease)(struct file_lock *);
 
 locking rules:
 
@@ -435,6 +436,7 @@ lm_notify:		yes		yes			no
 lm_grant:		no		no			no
 lm_break:		yes		no			no
 lm_change		yes		no			no
+lm_breaker_owns_lease:	no		no			no
 ==========		=============	=================	=========
 
 buffer_head
diff --git a/fs/locks.c b/fs/locks.c
index b8a31c1c4fff3..a3f186846e93e 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1557,6 +1557,9 @@ static bool leases_conflict(struct file_lock *lease, struct file_lock *breaker)
 {
 	bool rc;
 
+	if (lease->fl_lmops->lm_breaker_owns_lease
+			&& lease->fl_lmops->lm_breaker_owns_lease(lease))
+		return false;
 	if ((breaker->fl_flags & FL_LAYOUT) != (lease->fl_flags & FL_LAYOUT)) {
 		rc = false;
 		goto trace;
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 0e75f7fb5fec0..a6d73aa51ce4e 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -2302,6 +2302,8 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 	}
 	check_if_stalefh_allowed(args);
 
+	rqstp->rq_lease_breaker = (void **)&cstate->clp;
+
 	trace_nfsd_compound(rqstp, args->opcnt);
 	while (!status && resp->opcnt < args->opcnt) {
 		op = &args->ops[resp->opcnt++];
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index c107caa565254..f71e5590967bb 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4522,6 +4522,19 @@ nfsd_break_deleg_cb(struct file_lock *fl)
 	return ret;
 }
 
+static bool nfsd_breaker_owns_lease(struct file_lock *fl)
+{
+	struct nfs4_delegation *dl = fl->fl_owner;
+	struct svc_rqst *rqst;
+	struct nfs4_client *clp;
+
+	if (!i_am_nfsd())
+		return NULL;
+	rqst = kthread_data(current);
+	clp = *(rqst->rq_lease_breaker);
+	return dl->dl_stid.sc_client == clp;
+}
+
 static int
 nfsd_change_deleg_cb(struct file_lock *onlist, int arg,
 		     struct list_head *dispose)
@@ -4533,6 +4546,7 @@ nfsd_change_deleg_cb(struct file_lock *onlist, int arg,
 }
 
 static const struct lock_manager_operations nfsd_lease_mng_ops = {
+	.lm_breaker_owns_lease = nfsd_breaker_owns_lease,
 	.lm_break = nfsd_break_deleg_cb,
 	.lm_change = nfsd_change_deleg_cb,
 };
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 2ab5569126b8a..36cdd81b6688a 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -88,6 +88,8 @@ int		nfsd_pool_stats_release(struct inode *, struct file *);
 
 void		nfsd_destroy(struct net *net);
 
+bool		i_am_nfsd(void);
+
 struct nfsdfs_client {
 	struct kref cl_ref;
 	void (*cl_release)(struct kref *kref);
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index ca9fd348548b8..4f588c0eaaf44 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -601,6 +601,11 @@ static const struct svc_serv_ops nfsd_thread_sv_ops = {
 	.svo_module		= THIS_MODULE,
 };
 
+bool i_am_nfsd()
+{
+	return kthread_func(current) == nfsd;
+}
+
 int nfsd_create_serv(struct net *net)
 {
 	int error;
@@ -1011,6 +1016,7 @@ nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
 		*statp = rpc_garbage_args;
 		return 1;
 	}
+	rqstp->rq_lease_breaker = NULL;
 	/*
 	 * Give the xdr decoder a chance to change this if it wants
 	 * (necessary in the NFSv4.0 compound case)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 45cc10cdf6ddd..70a0ac7b8f66a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1045,6 +1045,7 @@ struct lock_manager_operations {
 	bool (*lm_break)(struct file_lock *);
 	int (*lm_change)(struct file_lock *, int, struct list_head *);
 	void (*lm_setup)(struct file_lock *, void **);
+	bool (*lm_breaker_owns_lease)(struct file_lock *);
 };
 
 struct lock_manager {
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index fd390894a5849..abf4a57ce4a7d 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -299,6 +299,7 @@ struct svc_rqst {
 	struct net		*rq_bc_net;	/* pointer to backchannel's
 						 * net namespace
 						 */
+	void **			rq_lease_breaker; /* The v4 client breaking a lease */
 };
 
 #define SVC_NET(rqst) (rqst->rq_xprt ? rqst->rq_xprt->xpt_net : rqst->rq_bc_net)
-- 
2.25.1