in recent 7-STABLE: VOP_WRITE...is not exclusive locked but should be

[Kostik Belousov]

On Thu, Mar 19, 2009 at 10:01:44AM -0400, John Baldwin wrote:
> On Thursday 19 March 2009 8:05:34 am Tim Chase wrote:
> > Hello,
> > 
> > I have a system that had been running quite well with an oldish 7-STABLE
> > (from around August 7, 2008) but has started deadlocking within the past
> > week or so.
> > 
> > I updated the kernel to a newer 7-STABLE (Mar 15, 2009) and enabled
> > INVARIANTS, INVARIANT_SUPPORT, WITNESS, DEBUG_LOCKS DEBUG_VFS_LOCKS and
> > DIAGNOSTIC and the message indicated in the subject line has now appeared
> > 3 times as shown below.  Is this something to be terribly concerned about?
> > Is there anything I can to to further track down the cause?  Since the
> > system is a production mail server, I have it set to not drop into DDB
> > when this happens.
> > 
> > The machine is a 4-core Xeon X5450 with 8G of RAM running FreeBSD
> > amd64 and in userland it's pretty much just cyrus imapd and apache/php.
> > The file systems are all ZFS on a bunch of SAS drives connected to a
> > LSI Logic 1068 controller.
> > 
> > As to the deadlock that started this exercise, if the machine follows its
> > recent pattern, that should happen within the next 2-4 hours.
> 
> Err, the vn_write() routine should be using an exclusive vnode lock:
> 
> vn_write()
> {
> 
> 	...
> 	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
> 	if ((flags & FOF_OFFSET) == 0)
> 		uio->uio_offset = fp->f_offset;
> 	ioflag |= sequential_heuristic(uio, fp);
> #ifdef MAC
> 	error = mac_check_vnode_write(active_cred, fp->f_cred, vp);
> 	if (error == 0)
> #endif
> 		error = VOP_WRITE(vp, uio, ioflag, fp->f_cred);
> 	...
> }
> 
> Can you check your /sys/kern/vfs_vnops.c and verify that LK_EXCLUSIVE is 
> present in your vn_write() routine?  If so, then perhaps run memtest?

Note that this happens on the ZFS. Might be, ZFS unlocks the vnode and
then relocks it with some invalid flags ?
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