vgsp-sema: only a real session end may request the discovery flush (ISSUE-0002)

A redundant channel delete (a FREE for a handle that never registered, or
a repeated delete after the session already ended) found the channel set
empty while the next client was already starting and re-armed the flush,
which then executed mid-startup and wiped that client's discovery state
(and dropped its pending releases): the client spun at its first channel.
Track whether a session's channel has registered since the last flush and
request the flush only on the true existed->empty transition; redundant
deletes are inert.

1 files changed, 15 insertions, 6 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 3b56c36..715e458 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -406,6 +406,7 @@ static u32 svc_ring_n;
  * rebuild start from the same empty state as a fresh boot.
  */
 static u8 svc_sess_flush;
+static u8 svc_sess_active;	/* a channel of a session has registered (until flush) */
 static unsigned long svc_ring_done;	/* CE ranks whose ring is pinned (session state) */
 static u8 svc_pb_passes;
 static u64 svc_pb_last;
@@ -925,6 +926,7 @@ void gsp_sema_service_channel_add(const struct sema_channel_desc *desc)
 			ch->gr_index = rank;
 		}
 		ch->valid = true;
+		svc_sess_active = 1;
 		ch->h_object = desc->h_object;
 		ch->engine_type = desc->engine_type;
 		ch->cid = desc->cid;
@@ -986,14 +988,21 @@ void gsp_sema_service_channel_del(u32 h_object)
 	 * session in a new UVM VA space; its discovery state must not inherit
 	 * this session's map/pins/page-directory latch. Request the flush
 	 * here; it executes at the next rebuild (the only writer of that
-	 * state) just like a fresh boot would start empty.
+	 * state) just like a fresh boot would start empty. Only the transition
+	 * from "a session existed" to "empty" may request it: redundant
+	 * deletes for handles that never registered would otherwise re-flush
+	 * (and wipe) a session that started after the real one ended.
 	 */
-	for (i = 0; i < SVC_MAX_CHANNELS; i++) {
-		if (svc.chan[i].valid)
-			break;
+	if (svc_sess_active) {
+		for (i = 0; i < SVC_MAX_CHANNELS; i++) {
+			if (svc.chan[i].valid)
+				break;
+		}
+		if (i == SVC_MAX_CHANNELS) {
+			svc_sess_active = 0;
+			svc_sess_flush = 1;
+		}
 	}
-	if (i == SVC_MAX_CHANNELS)
-		svc_sess_flush = 1;
 	spin_unlock_irqrestore(&svc.chan_lock, flags);
 
 	/*