r576b diag: witness the recovery-release target (sema-fake lines)

The r575 atomics wedge: a UVM tracker wait for payload 34 on its channel
tracking semaphore stalled at 25 while the pump consumed the channel's
remaining ring entries via the unreadable-entry grace/fake ladder and the
client's wait never cleared (a manual exact-slot delivery of 34 via
poke_guest unblocked it and the client completed green). The recovery
release chosen by svc_fake_release is the suspect: its pool target is
last_rel_va, learned from readable pushes, and a foreign release VA
appearing there would send every later recovery to the wrong semaphore.
Log every authored/queued recovery with its chosen target and payload
(bounded, gsp_sema_dbg) so the next draw names the divergence.

1 files changed, 17 insertions, 0 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index dfe7c3f..d2c7eaf 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -8503,6 +8503,7 @@ static u64 svc_rel_va_seen;
  * on every decoded release regardless of its target.
  */
 static u32 svc_rel_count;
+static u32 svc_fake_rel_log;	/* r576b DIAG: sema-fake witness budget */
 static u32 svc_dbg_streams;
 static u32 svc_chan_put_log;
 /* ISSUE-0002 (r55): per-rank put-snapshot throttle (ch is a local copy). */
@@ -16554,6 +16555,22 @@ static bool svc_fake_release(struct nv_vgpu_device *vgpu, struct svc_channel *ch
 		svc_pending_add(pool_va, deliver, 0);
 		svc.releases_forwarded++;
 	}
+	/*
+	 * r576b DIAG: witness every authored/queued recovery release and the
+	 * target it chose. The r575 atomics wedge (a UVM tracker wait for
+	 * payload 34 that stalled at 25 while the ring was consumed) needs
+	 * this to prove which VA the fakes targeted when the client's pool
+	 * stopped advancing - last_rel_va is learned from readable pushes and
+	 * a foreign release VA there would send every later recovery to the
+	 * wrong semaphore.
+	 */
+	if (gsp_sema_dbg && svc_fake_rel_log < 256) {
+		svc_fake_rel_log++;
+		pr_info("sema-fake: h=0x%x pool=0x%llx deliver=%u delivered=%d have_pa=%d last_rel=0x%llx exp=%u\n",
+			ch->h_object, pool_va, deliver, delivered ? 1 : 0,
+			have_pa ? 1 : 0, ch->last_rel_va,
+			ch->expected_sem_payload);
+	}
 	svc.releases_faked++;
 	svc_rel_count++;
 	ch->expected_sem_payload++;