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

[John Baldwin]

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?

-- 
John Baldwin