[PATCH v2 3/5] ceph: add wait_list_lock for wait-list serialization

[Xiubo Li via B4 Relay]

From: Xiubo Li <xiubo.li@xxxxxxxxx>

Add a dedicated spinlock to protect the waiting_for_map and
s_waiting lists, which are currently serialized by mdsc->mutex.
This is a preparatory step for removing mdsc->mutex from the
kick_requests() path: xa_for_each() is internally locked and the
per-request filter checks are lockless, so only list_del_init()
needs external protection.

Signed-off-by: Xiubo Li <xiubo.li@xxxxxxxxx>
---
 fs/ceph/mds_client.c | 18 +++++++++++++++++-
 fs/ceph/mds_client.h |  3 +++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 239ed34886f9..a250938f32d3 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -3669,7 +3669,9 @@ static void __do_request(struct ceph_mds_client *mdsc,
 			doutc(cl, "no mdsmap, waiting for map\n");
 			trace_ceph_mdsc_suspend_request(mdsc, session, req,
 							ceph_mdsc_suspend_reason_no_mdsmap);
+			spin_lock(&mdsc->wait_list_lock);
 			list_add(&req->r_wait, &mdsc->waiting_for_map);
+			spin_unlock(&mdsc->wait_list_lock);
 			return;
 		}
 		if (!(mdsc->fsc->mount_options->flags &
@@ -3692,7 +3694,9 @@ static void __do_request(struct ceph_mds_client *mdsc,
 		doutc(cl, "no mds or not active, waiting for map\n");
 		trace_ceph_mdsc_suspend_request(mdsc, session, req,
 						ceph_mdsc_suspend_reason_no_active_mds);
+		spin_lock(&mdsc->wait_list_lock);
 		list_add(&req->r_wait, &mdsc->waiting_for_map);
+		spin_unlock(&mdsc->wait_list_lock);
 		return;
 	}
 
@@ -3740,9 +3744,12 @@ static void __do_request(struct ceph_mds_client *mdsc,
 			if (ceph_test_mount_opt(mdsc->fsc, CLEANRECOVER)) {
 				trace_ceph_mdsc_suspend_request(mdsc, session, req,
 								ceph_mdsc_suspend_reason_rejected);
+				spin_lock(&mdsc->wait_list_lock);
 				list_add(&req->r_wait, &mdsc->waiting_for_map);
-			} else
+				spin_unlock(&mdsc->wait_list_lock);
+			} else {
 				err = -EACCES;
+			}
 			goto out_session;
 		}
 
@@ -3757,7 +3764,9 @@ static void __do_request(struct ceph_mds_client *mdsc,
 		}
 		trace_ceph_mdsc_suspend_request(mdsc, session, req,
 						ceph_mdsc_suspend_reason_session);
+		spin_lock(&mdsc->wait_list_lock);
 		list_add(&req->r_wait, &session->s_waiting);
+		spin_unlock(&mdsc->wait_list_lock);
 		goto out_session;
 	}
 
@@ -3850,7 +3859,9 @@ static void __wake_requests(struct ceph_mds_client *mdsc,
 	struct ceph_mds_request *req;
 	LIST_HEAD(tmp_list);
 
+	spin_lock(&mdsc->wait_list_lock);
 	list_splice_init(head, &tmp_list);
+	spin_unlock(&mdsc->wait_list_lock);
 
 	while (!list_empty(&tmp_list)) {
 		req = list_entry(tmp_list.next,
@@ -3892,7 +3903,9 @@ static void kick_requests(struct ceph_mds_client *mdsc, int mds)
 		if (req->r_session &&
 		    req->r_session->s_mds == mds) {
 			doutc(cl, " kicking tid %llu\n", req->r_tid);
+			spin_lock(&mdsc->wait_list_lock);
 			list_del_init(&req->r_wait);
+			spin_unlock(&mdsc->wait_list_lock);
 			trace_ceph_mdsc_resume_request(mdsc, req);
 			__do_request(mdsc, req);
 		}
@@ -6359,6 +6372,7 @@ int ceph_mdsc_init(struct ceph_fs_client *fsc)
 	mdsc->snap_realms = RB_ROOT;
 	INIT_LIST_HEAD(&mdsc->snap_empty);
 	spin_lock_init(&mdsc->snap_empty_lock);
+	spin_lock_init(&mdsc->wait_list_lock);
 #if BITS_PER_LONG == 64
 	xa_init(&mdsc->request_tree);
 #else
@@ -6445,7 +6459,9 @@ static void wait_requests(struct ceph_mds_client *mdsc)
 		mutex_lock(&mdsc->mutex);
 		while ((req = __get_oldest_req(mdsc))) {
 			doutc(cl, "timed out on tid %llu\n", req->r_tid);
+			spin_lock(&mdsc->wait_list_lock);
 			list_del_init(&req->r_wait);
+			spin_unlock(&mdsc->wait_list_lock);
 			__unregister_request(mdsc, req);
 		}
 	}
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index c2de551607e3..0a9f89498604 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -534,6 +534,9 @@ struct ceph_mds_client {
 	struct list_head        snap_empty;
 	int			num_snap_realms;
 	spinlock_t              snap_empty_lock;  /* protect snap_empty */
+	spinlock_t              wait_list_lock;   /* protect waiting_for_map
+						   * and s_waiting lists
+						   */
 
 	u64                    last_tid;      /* most recent mds request */
 	atomic64_t             oldest_tid;    /* oldest incomplete mds request,

-- 
2.53.0