Fix boundry condition in lock management:

 Alfred, I took a look at retry_blockingfilelocklist() and the
 solution seemed  simple enough. Please correct me if I am wrong.
 It seems said routine doesn't  take into account boundary conditions
 when putting back file_lock entries into the blocked lock-list.
 Specifically, it fails when the file_lock being put back is the
 last element in the list, and when it is the only element in the
 list.  I've included a patch below.

 Basically, it introduces another variable: pfl, which keeps track
 of the list  item before ifl. That way if nfl is NULL, ifl gets
 inserted after pfl. If pfl  is also NULL, then it gets inserted
 at the head of the list (since it was the  only element in the
 list).

Submitted by: Mike Makonnen <mike_makonnen@yahoo.com>
Tested by: Thomas Quinot <thomas@cuivre.fr.eu.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/usr.sbin/rpc.lockd/lockd_lock.c b/usr.sbin/rpc.lockd/lockd_lock.c
index f898782..b80c243 100644
--- a/usr.sbin/rpc.lockd/lockd_lock.c
+++ b/usr.sbin/rpc.lockd/lockd_lock.c
@@ -1226,11 +1226,12 @@ void
 retry_blockingfilelocklist(void)
 {
 	/* Retry all locks in the blocked list */
-	struct file_lock *ifl, *nfl; /* Iterator */
+	struct file_lock *ifl, *nfl, *pfl; /* Iterator */
 	enum partialfilelock_status pflstatus;
 
 	debuglog("Entering retry_blockingfilelocklist\n");
 
+	pfl = NULL;
 	ifl = LIST_FIRST(&blockedlocklist_head);
 	debuglog("Iterator choice %p\n",ifl);
 
@@ -1241,6 +1242,7 @@ retry_blockingfilelocklist(void)
 		 */
 		nfl = LIST_NEXT(ifl, nfslocklist);
 		debuglog("Iterator choice %p\n",ifl);
+		debuglog("Prev iterator choice %p\n",pfl);
 		debuglog("Next iterator choice %p\n",nfl);
 
 		/*
@@ -1260,11 +1262,20 @@ retry_blockingfilelocklist(void)
 		} else {
 			/* Reinsert lock back into same place in blocked list */
 			debuglog("Replacing blocked lock\n");
-			LIST_INSERT_BEFORE(nfl, ifl, nfslocklist);
+			if (pfl != NULL)
+				LIST_INSERT_AFTER(pfl, ifl, nfslocklist);
+			else
+				/* ifl is the only elem. in the list */
+				LIST_INSERT_HEAD(&blockedlocklist_head, ifl, nfslocklist);
 		}
 
 		/* Valid increment behavior regardless of state of ifl */
 		ifl = nfl;
+		/* if a lock was granted incrementing pfl would make it nfl */
+		if (pfl != NULL && (LIST_NEXT(pfl, nfslocklist) != nfl))
+			pfl = LIST_NEXT(pfl, nfslocklist);
+		else
+			pfl = LIST_FIRST(&blockedlocklist_head);
 	}
 
 	debuglog("Exiting retry_blockingfilelocklist\n");