Re: [PATCH] Re: zero-filed page on VOP_PUTPAGES

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Aug 26, 2011 at 01:07:43AM +0200, Emmanuel Dreyfus wrote:
> [...]
> +        */
> +       if ((locked = VOP_ISLOCKED(vp)) != LK_EXCLUSIVE)
> +               vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);

You can't use VOP_ISLOCKED this way (it's basically there to be
used in KASSERT()): for ufs, this is genfs_islocked() which 
calls rw_write_held() and rw_read_held(). from rwlock(9):
     rw_read_held(rw)

     rw_lock_held(rw)

           Test the lock's condition and return non-zero if the lock is held
           (potentially by the current LWP) and matches the specified condi-
           tion.  Otherwise, return zero.

           These functions must never be used to make locking decisions at run
           time: they are provided only for diagnostic purposes.

The point is that VOP_ISLOCKED() will tell you if the vnode is
locked or not, but you don't know if it's locked by the curlwp, or
by another lwp.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--