close() of an flock'd file is not atomic

[John Baldwin]

On Monday, July 09, 2012 4:40:07 pm Konstantin Belousov wrote:
> On Mon, Jul 09, 2012 at 11:38:15AM -0400, John Baldwin wrote:
> > Here now is the tested version of the actual fix after the vn_open_vnode()
> > changes were committed.  This is hopefully easier to parse now.
> > 
> > http://www.FreeBSD.org/~jhb/patches/flock_open_close4.patch
> 
> Do you need atomic op to set FHASLOCK in vn_open_cred ? I do not think
> *fp can be shared with other thread there.

Oh, that's true.  I had just preserved it from the original code.

> I thought that vrele() call in vn_closefile() would need a
> vn_start_write() or vn_start_secondary_write() dance around it, but
> now I believe it is not needed, since ufs_inactive() handles start of
> secondary writes on its own. Still, it would be good if Peter could test
> the patch with snapshotting load just be to safe there.

Ok.  I'm happy to have pho@ test it, but the test will have to use file 
locking along with snapshots to exercise this case.

-- 
John Baldwin