On Sun, Jun 12, 2011 at 3:38 PM, Borislav Petkov<bp@xxxxxxxxx> wrote:
> On Thu, Jun 09, 2011 at 05:36:42PM -0400, Luck, Tony wrote:
>> From: Tony Luck<tony.luck@xxxxxxxxx>
>>
>> Existing user return notifier mechanism is designed to catch a specific
>> cpu just as it returns to run any task in user mode. We also need a
>> mechanism to catch a specific task.
>
> Why do we need that? I mean, in the remaining patches we end up either
> running memory_failure() or sending signals to a task. Can't we do it
> all in the user return notifier and not have a different notifier for
> each policy?
Unless I'm mis-reading the user-return-notifier code, it is possible that
we'll context switch before we get to the notifier. At that point the
user-return-notifier TIF bit is passed on from our task to the newly
run-able task. But our task is still viable, so another cpu could grab
it and start running it ... then we have a race ... will the new task
that inherited the notifier unmap the page fast enough, or will there
be a loud BANG as the original task runs right into the machine
check again.