On Wed, Nov 04, 2009 at 02:37:28PM +0100, Andi Kleen wrote: > On Wed, Nov 04, 2009 at 03:17:36PM +0200, Michael S. Tsirkin wrote: > > On Wed, Nov 04, 2009 at 02:15:33PM +0100, Andi Kleen wrote: > > > On Wed, Nov 04, 2009 at 03:08:28PM +0200, Michael S. Tsirkin wrote: > > > > On Wed, Nov 04, 2009 at 01:59:57PM +0100, Andi Kleen wrote: > > > > > > Fine? > > > > > > > > > > I cannot say -- are there paths that could drop the device beforehand? > > > > > > > > Do you mean drop the mm reference? > > > > > > No the reference to the device, which owns the mm for you. > > > > The device is created when file is open and destroyed > > when file is closed. So I think the fs code handles the > > reference counting for me: it won't call file cleanup > > callback while some userspace process has the file open. > > Right? > > Yes. > > But the semantics when someone inherits such a fd through exec > or through file descriptor passing would be surely "interesting" > You would still do IO on the old VM. > > I guess it would be a good way to confuse memory accounting schemes > or administrators @) > It would be all saner if this was all a single atomic step. > > -Andi I have this atomic actually. A child process will first thing do SET_OWNER: this is required before any other operation. SET_OWNER atomically (under mutex) does two things: - check that there is no other owner - get mm and set current process as owner I hope this addresses your concern? -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
