vgsp-gr r553: the dstpend launch-defer window is absolute, not sliding

r551 soak evidence (victory_strided, same boot as a green battery): the
client's init copies keep failing -ENOENT and are retried by the pump;
every retry re-noted its destination page and re-freshened the r541
dstpend record, so svc_gr_dstpend_overlap() never lapsed and the launch
guard deferred the launch forever: "GR busy-defer timeout -> hold
8000 ms" every ~4 s for 427 s, zero GR LAUNCH submitted, client at 100%
CPU.

Stamp a page's record once per failure episode: an existing record inside
its 10 s window is not re-stamped (the window stays absolute from the first
unexecuted write); an expired record is re-stamped for a genuinely new
episode. The launch then forwards best-effort at the bound exactly as the
guard's own comment promises ("bounded by the same busy-defer + gr_hold
machinery ... it can never hang the launch").

1 files changed, 16 insertions, 0 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 52819da..91f1df9 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -7921,6 +7921,22 @@ static void svc_dstpend_note(u64 va)
 		return;
 	for (i = 0; i < svc_dstpend_n; i++) {
 		if (svc_dstpend[i].va_page == page) {
+			/*
+			 * r553: the window is ABSOLUTE from the first failed
+			 * attempt for this page, never re-freshened by the
+			 * retries. The retried decode of a copy that cannot
+			 * resolve re-notes its destination on every pass; with
+			 * a sliding stamp the record never expired and the r541
+			 * launch guard deferred the launch forever - r551 soak:
+			 * victory_strided repeated "GR busy-defer timeout ->
+			 * hold 8000 ms" every ~4 s for 427 s with the launch
+			 * never forwarded (the copies' -ENOENT retries kept the
+			 * note fresh). A record older than the window is
+			 * refreshed only when a NEW failure episode starts.
+			 */
+			if (time_before(jiffies, svc_dstpend[i].since +
+					msecs_to_jiffies(SVC_DSTPEND_MS)))
+				return;
 			svc_dstpend[i].since = jiffies;
 			return;
 		}