[PATCH 5.10.y 1/3] nfsd: use workqueue enable/disable APIs for v4_end_grace sync

[Sasha Levin <sashal@kernel.org>]

From: NeilBrown <neil@brown.name>

[ Upstream commit 27e383ddeb3c88e20874c545285f2dce1a98f56a ]

"nfsd: provide locking for v4_end_grace" introduced a
client_tracking_active flag protected by nn->client_lock to prevent
the laundromat from being scheduled before client tracking
initialization or after shutdown begins. That commit is suitable for
backporting to LTS kernels that predate commit 86898fa6b8cd
("workqueue: Implement disable/enable for (delayed) work items").

However, the workqueue subsystem in recent kernels provides
enable_delayed_work() and disable_delayed_work_sync() for this
purpose. Using this mechanism enable us to remove the
client_tracking_active flag and associated spinlock operations
while preserving the same synchronization guarantees, which is
a cleaner long-term approach.

Signed-off-by: NeilBrown <neil@brown.name>
Tested-by: Li Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: 9b57793863f6 ("nfsd: dedup nfs4_client_to_reclaim inserts")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/netns.h     |  1 -
 fs/nfsd/nfs4state.c | 22 +++++++++-------------
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index be0c8f1ce4e3e..139d9370f27f2 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -65,7 +65,6 @@ struct nfsd_net {
 	struct lock_manager nfsd4_manager;
 	bool grace_ended;
 	bool grace_end_forced;
-	bool client_tracking_active;
 	time64_t boot_time;
 
 	struct dentry *nfsd_client_dir;
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index c61e1a4ab620c..7095fa43fcf36 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -5928,14 +5928,14 @@ bool nfsd4_force_end_grace(struct nfsd_net *nn)
 {
 	if (!nn->client_tracking_ops)
 		return false;
-	spin_lock(&nn->client_lock);
-	if (nn->grace_ended || !nn->client_tracking_active) {
-		spin_unlock(&nn->client_lock);
+	if (READ_ONCE(nn->grace_ended))
 		return false;
-	}
+	/* laundromat_work must be initialised now, though it might be disabled */
 	WRITE_ONCE(nn->grace_end_forced, true);
+	/* mod_delayed_work() doesn't queue work after
+	 * nfs4_state_shutdown_net() has called disable_delayed_work_sync()
+	 */
 	mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
-	spin_unlock(&nn->client_lock);
 	return true;
 }
 
@@ -8187,7 +8187,6 @@ static int nfs4_state_create_net(struct net *net)
 	nn->boot_time = ktime_get_real_seconds();
 	nn->grace_ended = false;
 	nn->grace_end_forced = false;
-	nn->client_tracking_active = false;
 	nn->nfsd4_manager.block_opens = true;
 	INIT_LIST_HEAD(&nn->nfsd4_manager.list);
 	INIT_LIST_HEAD(&nn->client_lru);
@@ -8202,6 +8201,8 @@ static int nfs4_state_create_net(struct net *net)
 	INIT_LIST_HEAD(&nn->blocked_locks_lru);
 
 	INIT_DELAYED_WORK(&nn->laundromat_work, laundromat_main);
+	/* Make sure this cannot run until client tracking is initialised */
+	disable_delayed_work(&nn->laundromat_work);
 	INIT_WORK(&nn->nfsd_shrinker_work, nfsd4_state_shrinker_worker);
 	get_net(net);
 
@@ -8265,9 +8266,7 @@ nfs4_state_start_net(struct net *net)
 	locks_start_grace(net, &nn->nfsd4_manager);
 	nfsd4_client_tracking_init(net);
 	/* safe for laundromat to run now */
-	spin_lock(&nn->client_lock);
-	nn->client_tracking_active = true;
-	spin_unlock(&nn->client_lock);
+	enable_delayed_work(&nn->laundromat_work);
 	if (nn->track_reclaim_completes && nn->reclaim_str_hashtbl_size == 0)
 		goto skip_grace;
 	printk(KERN_INFO "NFSD: starting %lld-second grace period (net %x)\n",
@@ -8314,10 +8313,7 @@ nfs4_state_shutdown_net(struct net *net)
 
 	unregister_shrinker(&nn->nfsd_client_shrinker);
 	cancel_work_sync(&nn->nfsd_shrinker_work);
-	spin_lock(&nn->client_lock);
-	nn->client_tracking_active = false;
-	spin_unlock(&nn->client_lock);
-	cancel_delayed_work_sync(&nn->laundromat_work);
+	disable_delayed_work_sync(&nn->laundromat_work);
 	locks_end_grace(&nn->nfsd4_manager);
 
 	INIT_LIST_HEAD(&reaplist);
-- 
2.53.0