Re: Giant pushdown in kern_descrip.c rev 1.128

* Don Lewis <truckman_at_FreeBSD.org> [030617 12:00] wrote:
> It's not legal to attempt to aquire Giant in fdrop_locked(), while
> FILE_LOCK() is held.  The problem is that FILE_LOCK uses the mutex pool,
> which should only be used for leaf mutexes.
> 
> It also looks like there is a potential for a lock order reversal if
> some callers aquire Giant before FILE_LOCK() and fdrop_locked() does the
> opposite.
> 
> It also appears that witness ignores the mutex pool ...

Yes, but I think the fix is as simple as just dropping the FILE_LOCK
after the decrement as we're the last holders of it, can you try
this:

Index: kern_descrip.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/kern_descrip.c,v
retrieving revision 1.199
diff -u -r1.199 kern_descrip.c
--- kern_descrip.c	11 Jun 2003 00:56:55 -0000	1.199
+++ kern_descrip.c	17 Jun 2003 19:07:01 -0000
_at__at_ -2003,6 +2003,7 _at__at_
 		FILE_UNLOCK(fp);
 		return (0);
 	}
+	FILE_UNLOCK(fp);
 	mtx_lock(&Giant);
 	if (fp->f_count < 0)
 		panic("fdrop: count < 0");
_at__at_ -2012,10 +2013,8 _at__at_
 		lf.l_len = 0;
 		lf.l_type = F_UNLCK;
 		vp = fp->f_data;
-		FILE_UNLOCK(fp);
 		(void) VOP_ADVLOCK(vp, (caddr_t)fp, F_UNLCK, &lf, F_FLOCK);
-	} else
-		FILE_UNLOCK(fp);
+	}
 	if (fp->f_ops != &badfileops)
 		error = fo_close(fp, td);
 	else