21 Sep
2020
21 Sep
'20
7:39 a.m.
On Sun, Sep 20 2020 at 10:42, Linus Torvalds wrote:
On Sun, Sep 20, 2020 at 10:40 AM Thomas Gleixner tglx@linutronix.de wrote:
I think the more obvious solution is to split the whole exercise:
schedule() prepare_switch() unmap()
switch_to() finish_switch() map()Yeah, that looks much easier to explain. Ack.
So far so good, but Peter Z. just pointed out to me that I completely missed the fact that this cannot work.
If a task is migrated to a different CPU then the mapping address will change which will explode in colourful ways.
On RT kernels this works because we ping the task to the CPU via migrate_disable(). On a !RT kernel migrate_disable() maps to preempt_disable() which brings us back to square one.
/me goes back to the drawing board.
Thanks,
tglx