When the MNTK_EXTENDED_SHARED mount option was added, some filesystems were

changed to defer the setting of VN_LOCK_ASHARE() (which clears LK_NOSHARE
in the vnode lock's flags) until after they had determined if the vnode was
a FIFO.  This occurs after the vnode has been inserted a VFS hash or some
similar table, so it is possible for another thread to find this vnode via
vget() on an i-node number and block on the vnode lock.  If the lockmgr
interlock (vnode interlock for vnode locks) is not held when clearing the
LK_NOSHARE flag, then the lk_flags field can be clobbered.  As a result
the thread blocked on the vnode lock may never get woken up.  Fix this by
holding the vnode interlock while modifying the lock flags in this case.

MFC after:	3 days

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index c099732398fd..aa9f19ac4be6 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -1577,7 +1577,9 @@ ffs_vgetf(mp, ino, flags, vpp, ffs_flags)
 	 */
 	if (vp->v_type != VFIFO) {
 		/* FFS supports shared locking for all files except fifos. */
+		VI_LOCK(vp);
 		VN_LOCK_ASHARE(vp);
+		VI_UNLOCK(vp);
 	}
 
 	/*