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? > > > > > (as in do you hold a reference to it?) > > > > By design I think I always have a reference to mm before I use it. > > > > This works like this: > > ioctl SET_OWNER - calls get_task_mm, I think this gets a reference to mm > > ioctl SET_BACKEND - checks that SET_OWNER was run, starts virtqueue > > ioctl RESET_OWNER - stops virtqueues, drops the reference to mm > > file close - stops virtqueues, if we still have it then drops mm > > > > This is why I think I can call use_mm/unuse_mm while virtqueue is running, > > safely. > > Makes sense? > > Do you protect against another thread doing RESET_OWNER in parallel while > RESET_OWNER runs? Yes, I have a mutex in the device for that. Same with SET_BACKEND. > -Andi > > -- > ak@xxxxxxxxxxxxxxx -- Speaking for myself only. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
