Earlier FREF() for dupfdopen()

[Martin Pieuchot]

Instead of incrementing `f_count' directly, we'll use the reference that
will be returned by fd_getfile(9).  For that call FREF(9) earlier.

ok?

Index: kern/kern_descrip.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_descrip.c,v
retrieving revision 1.147
diff -u -p -r1.147 kern_descrip.c
--- kern/kern_descrip.c 9 Apr 2018 13:59:03 -0000       1.147
+++ kern/kern_descrip.c 10 Apr 2018 10:53:33 -0000
@@ -1297,22 +1297,26 @@ dupfdopen(struct proc *p, int indx, int 
         */
        if ((wfp = fd_getfile(fdp, dupfd)) == NULL)
                return (EBADF);
+       FREF(wfp);
 
        /*
         * Check that the mode the file is being opened for is a
         * subset of the mode of the existing descriptor.
         */
-       if (((mode & (FREAD|FWRITE)) | wfp->f_flag) != wfp->f_flag)
+       if (((mode & (FREAD|FWRITE)) | wfp->f_flag) != wfp->f_flag) {
+               FRELE(wfp, p);
                return (EACCES);
-       if (wfp->f_count == LONG_MAX-2)
+       }
+       if (wfp->f_count == LONG_MAX-2) {
+               FRELE(wfp, p);
                return (EDEADLK);
+       }
 
        fdp->fd_ofiles[indx] = wfp;
        fdp->fd_ofileflags[indx] = (fdp->fd_ofileflags[indx] & UF_EXCLOSE) |
            (fdp->fd_ofileflags[dupfd] & ~UF_EXCLOSE);
        if (ISSET(p->p_p->ps_flags, PS_PLEDGE))
                fdp->fd_ofileflags[indx] |= UF_PLEDGED;
-       wfp->f_count++;
        fd_used(fdp, indx);
        return (0);
 }