[PATCH] libmpathpersist: fix self-preemption when key has no active reservation

From: Cykang <[email protected]>

According to the SCSI-3 Persistent Reservations specification, when a
self-preemption is performed with a key that does not currently hold
an active reservation, the operation should be treated as an unregister
and should not fail.

The current code in do_mpath_persistent_reserve_out() does not check
whether the preempting key has a reservation before invoking the
self-preemption path. It unconditionally calls preempt_self() and
re-registers the key on the local paths, even when the key has no
reservation. This violates the SCSI-3 PR spec and can lead to
incorrect reservation states.

This patch moves the self-preemption check inside the conditional
block so that it only executes when the key matches, but does not
bypass the general preemption path for keys without a reservation.
With this change, the code will fall through to the common PR_OUT
handling (e.g., MPATH_PROUT_RES_SA or CLEAR_SA) when the key is not
reserved, allowing the storage target to properly process the
operation as an unregister.

Signed-off-by: Cykang <[email protected]>
Signed-off-by: Benjamin Marzinski <[email protected]>
---
 libmpathpersist/mpath_persist_int.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/libmpathpersist/mpath_persist_int.c b/libmpathpersist/mpath_persist_int.c
index 3091c5c2..6ca3b97d 100644
--- a/libmpathpersist/mpath_persist_int.c
+++ b/libmpathpersist/mpath_persist_int.c
@@ -841,6 +841,7 @@ int do_mpath_persistent_reserve_out(vector curmp, vector pathvec, int fd,
 	bool unregistering, preempting_reservation = false;
 	bool updated_prkey = false;
 	bool failed_paths = false;
+	bool self_preempt_unreg = false;
 
 	ret = mpath_get_map(curmp, fd, &mpp);
 	if (ret != MPATH_PR_SUCCESS)
@@ -961,13 +962,20 @@ int do_mpath_persistent_reserve_out(vector curmp, vector pathvec, int fd,
 						  rq_type, noisy);
 				break;
 			}
+			/* if we are preempting ourself */
+			if (memcmp(paramp->sa_key, paramp->key, 8) == 0) {
+				ret = preempt_self(mpp, rq_servact, rq_scope,
+						   rq_type, noisy, PREE_WORK_NONE);
+				break;
+			}
+		} else if (memcmp(paramp->sa_key, paramp->key, 8) == 0) {
+			/*
+			 * We are self-preempting, but we don't hold the
+			 * reservation. This will unregister the device
+			 */
+			self_preempt_unreg = true;
 		}
-		/* if we are preempting ourself */
-		if (memcmp(paramp->sa_key, paramp->key, 8) == 0) {
-			ret = preempt_self(mpp, rq_servact, rq_scope, rq_type,
-					   noisy, PREE_WORK_NONE);
-			break;
-		}
+
 		/* fallthrough */
 	case MPATH_PROUT_RES_SA:
 	case MPATH_PROUT_CLEAR_SA: {
@@ -1018,6 +1026,8 @@ int do_mpath_persistent_reserve_out(vector curmp, vector pathvec, int fd,
 	case MPATH_PROUT_PREE_AB_SA:
 		if (preempting_reservation)
 			update_prhold(mpp->alias, true);
+		else if (self_preempt_unreg)
+			update_prflag(mpp, 0);
 	}
 	return ret;
 }
-- 
2.46.1