vgsp-sema: session boundary is a client change, not the last channel closing (ISSUE-0002)

r79 regression from keeping the CeUtils scrubber channel registered
(client-scoped deletion): the session flush trigger required EVERY
channel to close, and the scrubber never closes, so the per-session
discovery reset never ran and the next client inherited the previous
session's map/pins (the r9 class; the first client of r79 wedged the
guest on an rwsem with no output).

The session is now keyed by owning client: channel_add records
svc_sess_client and requests the flush when a channel of a DIFFERENT
client registers while the previous session is live (then waits for it,
exactly like a pending flush); channel_del's flush trigger counts only
channels of the current session client, so persistent kernel/GPU-global
channels (the scrubber) no longer keep a dead session open.

1 files changed, 40 insertions, 10 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 638a866..9f967a5 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -451,6 +451,11 @@ static u32 svc_ring_n;
  */
 static u8 svc_sess_flush;
 static u8 svc_sess_active;	/* a channel of a session has registered (until flush) */
+static u32 svc_sess_client;	/* owning client of the current session's channels.
+				 * The kernel/GPU-global channels (the CeUtils
+				 * scrubber) persist across clients; the session
+				 * boundary is a change of owning client, not the
+				 * last channel closing (ISSUE-0002 r79). */
 static struct completion svc_sess_flush_done;	/* a pending flush has executed */
 static unsigned long svc_ring_done;	/* CE ranks whose ring is pinned (session state) */
 static u8 svc_pb_passes;
@@ -950,6 +955,20 @@ void gsp_sema_service_channel_add(const struct sema_channel_desc *desc)
 		WRITE_ONCE(svc_gr_content_rearm, true);
 
 	/*
+	 * ISSUE-0002 (r79): the kernel/GPU-global channels (the CeUtils
+	 * scrubber, entries=4096) persist across client sessions, so the
+	 * "last channel closed" trigger never fires once they are kept
+	 * registered. The real session boundary is a change of owning
+	 * client: when a channel of a new client registers while the
+	 * previous session's state is still live, request the same flush a
+	 * session end would (the wait below then lets svc_thread execute it
+	 * before this session's state exists).
+	 */
+	if (desc->h_client && svc_sess_client &&
+	    desc->h_client != svc_sess_client && svc_sess_active)
+		WRITE_ONCE(svc_sess_flush, 1);
+
+	/*
 	 * ISSUE-0002: a session-end flush may still be pending on svc_thread.
 	 * It must not execute after this session's state exists (r9: the
 	 * deferred flush ran between the first and second channel
@@ -1050,6 +1069,8 @@ void gsp_sema_service_channel_add(const struct sema_channel_desc *desc)
 		}
 		ch->valid = true;
 		svc_sess_active = 1;
+		if (desc->h_client)
+			svc_sess_client = desc->h_client;
 		ch->h_object = desc->h_object;
 		ch->h_client = desc->h_client;
 		ch->engine_type = desc->engine_type;
@@ -1136,19 +1157,28 @@ void gsp_sema_service_channel_del(u32 h_object, u32 h_client)
 		break;
 	}
 	/*
-	 * ISSUE-0002: when the last channel closes, the next client is a new
-	 * 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. 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.
+	 * ISSUE-0002: when the last channel of the current session's client
+	 * closes, the next client is a new 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. 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. Persistent kernel/GPU-global
+	 * channels (a different owning client, e.g. the CeUtils scrubber) do
+	 * not keep the session open (ISSUE-0002 r79: with the scrubber kept
+	 * registered the old all-channels check never fired and the next
+	 * client inherited stale state).
 	 */
 	if (svc_sess_active) {
 		for (i = 0; i < SVC_MAX_CHANNELS; i++) {
-			if (svc.chan[i].valid)
-				break;
+			if (!svc.chan[i].valid)
+				continue;
+			if (svc_sess_client && svc.chan[i].h_client &&
+			    svc.chan[i].h_client != svc_sess_client)
+				continue;
+			break;
 		}
 		if (i == SVC_MAX_CHANNELS) {
 			svc_sess_active = 0;