On 08/28/2011 04:56 PM, Joerg Roedel wrote:
On Sun, Aug 28, 2011 at 04:14:00PM +0300, Avi Kivity wrote: > On 08/26/2011 12:24 PM, Roedel, Joerg wrote: >> The biggest problem with this approach is that it has to happen in the >> context of the given process. Linux can't really modify an mm which >> which belong to another context in a safe way. >> > > Is use_mm() insufficient? Yes, it introduces a set of race conditions when a process that already has an mm wants to take over another processes mm temporarily (and when use_mm is modified to actually provide this functionality). It is only save when used from kernel-thread context. One example: Process A Process B Process C . . . . <-- takes A->mm . . and assignes as B->mm . . . --> Wants to take . . B->mm, but gets A->mm now
Good catch.
This can't be secured by a lock, because it introduces potential A->B<-->B->A lock problem when two processes try to take each others mm. It could probably be solved by a task->real_mm pointer, havn't thought about this yet...
Or a workqueue - you get a kernel thread context with a bit of boilerplate. -- error compiling committee.c: too many arguments to function -- 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
