[PATCH 1/2] locks: introduce i_blockleases to close lease races
J. Bruce Fields
bfields at fieldses.org
Sat Jun 11 22:08:26 MDT 2011
On Fri, Jun 10, 2011 at 05:34:46PM -0400, J. Bruce Fields wrote:
> On Fri, Jun 10, 2011 at 04:24:00PM -0400, Mimi Zohar wrote:
> > On Thu, 2011-06-09 at 20:10 -0400, J. Bruce Fields wrote:
> > > From: J. Bruce Fields <bfields at redhat.com>
> > >
> > > Since break_lease is called before i_writecount is incremented, there's
> > > a window between the two where a setlease call would have no way to know
> > > that an open is about to happen.
> > So unless the break_lease() call is moved from may_open() to after
> > nameidata_to_filp(), I don't see any other options.
> Actually, offhand I can't see why that wouldn't be OK.
> Though I think we still end up needing something like i_blockleases to
> handle unlink, link, rename, chown, and chmod.
Well, I guess there's a bizarre alternative that wouldn't require a new
What we care about is conflicts between read leases and operations that
modify the metadata of the inode or the set of names pointing to it.
As far as I can tell those operations all take the i_mutex either on the
inode itself or on the parents of one of its aliases.
So, you could prevent break_lease/setlease races by calling setlease
under *all* of those i_mutexes:
- take i_mutex on the inode
- take i_lock to prevent the set of aliases from changing
- take i_mutex for parent of each alias
- set the lease
- drop the parent i_mutexes, etc.
where the i_mutexes would all be taken with mutex_trylock, and we'd just
fail the whole setlease if any of them failed.
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