On Sun, 2011-06-12 at 15:12 -0400, J. Bruce Fields wrote: > On Sun, Jun 12, 2011 at 03:10:04PM -0400, Mimi Zohar wrote: > > On Sun, 2011-06-12 at 00:08 -0400, J. Bruce Fields wrote: > > > 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@xxxxxxxxxx> > > > > > > > > > > > > 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 > > > inode field: > > > > In lieu of adding a new inode field, another possible option, a bit > > kludgy, would be extending i_flock with an additional fl_flag > > FL_BLOCKLEASE. > > > > #define IS_BLOCKLEASE(fl) (fl->fl_flags & FL_BLOCKLEASE) > > Alas, that would mean adding and removing one of these file locks around > every single link, unlink, rename,.... > > --b. You're adding a call to break_lease() for each of them. Currently __break_lease() is only called if a lease exists. Assuming there aren't any existing leases, couldn't break_lease() call something like block_lease()? The free would be after the link, unlink, ..., completed/failed. (You wouldn't actually need to alloc/free the 'struct file_lock' each time, just set the pointer and reset to NULL.) Mimi > > > > Mimi > > > > > 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. > > > > > > ??? > > > > > > --b. > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
