The timer routine in the experimental NFS server did not acquire

the correct mutex when checking nfsv4root_lock. Although this
could be fixed by adding mutex lock/unlock calls, zack.kirsch at
isilon.com suggested a better fix that uses a non-blocking
acquisition of a reference count on nfsv4root_lock. This fix
allows the weird NFSLOCKSTATE(); NFSUNLOCKSTATE(); synchronization
to be deleted. This patch applies this fix.

Tested by:	zack.kirsch at isilon.com
MFC after:	2 weeks

1 files changed, 15 insertions, 0 deletions

diff --git a/sys/fs/nfs/nfs_commonsubs.c b/sys/fs/nfs/nfs_commonsubs.c
index dc5b2dc..6585fce 100644
--- a/sys/fs/nfs/nfs_commonsubs.c
+++ b/sys/fs/nfs/nfs_commonsubs.c
@@ -1824,6 +1824,21 @@ nfsv4_getref(struct nfsv4lock *lp, int *isleptp, void *mutex)
 }
 
 /*
+ * Get a reference as above, but return failure instead of sleeping if
+ * an exclusive lock is held.
+ */
+APPLESTATIC int
+nfsv4_getref_nonblock(struct nfsv4lock *lp)
+{
+
+	if ((lp->nfslock_lock & NFSV4LOCK_LOCK) != 0)
+		return (0);
+
+	lp->nfslock_usecnt++;
+	return (1);
+}
+
+/*
  * Test for a lock. Return 1 if locked, 0 otherwise.
  */
 APPLESTATIC int