[PATCH 17/21] NFSv4/pnfs: Dispatch CB_NOTIFY_DEVICEID DELETE to race recovery

Turn on the RFC 8881 Section 18.40.4 DELETE handling: a DELETE for a
deviceID that no live layout references keeps today's cheap behavior
(drop the cached device, no state-manager wake).  A DELETE for a
deviceID that live layouts still reference -- which a conformant
server never sends (Section 20.12) -- is deferred to the state
manager, which TEST_STATEIDs the referring layouts, recovers revoked
ones, and confirms or refutes the delete with GETDEVICEINFO.

The deferred case no longer unhashes the device immediately: if the
recovery concludes the DELETE was erroneous (the deviceID still
exists and a referring layout is still valid), the client keeps
using the cached device.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Benjamin Coddington <[email protected]>
---
 fs/nfs/callback_proc.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
index 1721c6dd2250..df4cbe7670e7 100644
--- a/fs/nfs/callback_proc.c
+++ b/fs/nfs/callback_proc.c
@@ -391,19 +391,34 @@ __be32 nfs4_callback_devicenotify(void *argp, void *resp,
 				continue;
 		}
 		/*
-		 * Unhash the cached device first so re-resolution cannot
-		 * re-pin the stale node, then re-point any references
-		 * pinned under live layouts (RFC 8881 Section 12.2.10).
-		 * The epoch bump lets an in-flight GETDEVICEINFO detect
-		 * that its reply may predate the change.
+		 * CHANGE: unhash the cached device first so re-resolution
+		 * cannot re-pin the stale node, then re-point any
+		 * references pinned under live layouts (RFC 8881 Section
+		 * 12.2.10).  The epoch bump lets an in-flight
+		 * GETDEVICEINFO detect that its reply may predate the
+		 * change.
+		 *
+		 * DELETE: a deviceID still referenced by a live layout
+		 * must never be deleted (Section 20.12), so a referenced
+		 * one may be racing layout revocation -- defer to the
+		 * state manager for the Section 18.40.4 recovery (this
+		 * thread cannot issue the fore-channel RPCs it needs).
+		 * Unreferenced: "no harm is done" -- drop the cached
+		 * device as before.
 		 */
-		if (dev->cbd_notify_type == NOTIFY_DEVICEID4_CHANGE)
+		if (dev->cbd_notify_type == NOTIFY_DEVICEID4_CHANGE) {
 			nfs4_deviceid_bump_change_epoch();
-		nfs4_delete_deviceid(ld, cps->clp, &dev->cbd_dev_id);
-		if (dev->cbd_notify_type == NOTIFY_DEVICEID4_CHANGE)
+			nfs4_delete_deviceid(ld, cps->clp, &dev->cbd_dev_id);
 			pnfs_layout_reresolve_deviceid_byclid(cps->clp, ld,
 							&dev->cbd_dev_id,
 							dev->cbd_immediate);
+		} else if (pnfs_layout_deviceid_referenced_byclid(cps->clp,
+						ld, &dev->cbd_dev_id)) {
+			pnfs_deviceid_delete_mark(cps->clp, ld,
+						  &dev->cbd_dev_id);
+		} else {
+			nfs4_delete_deviceid(ld, cps->clp, &dev->cbd_dev_id);
+		}
 	}
 	pnfs_put_layoutdriver(ld);
 out:
-- 
2.53.0