Xen RTDS scheduler locking

[Juergen Gross <jgross@xxxxxxxx>]

Looking at test failures with RTDS scheduler in Xen [1] I think I've found
a major issue with locking in the RTDS scheduler:

svc->flags seems to be not protected properly, as different locks are
used when doing non-atomic updates: prv->lock (the RTDS global lock),
or the per-scheduler-resource scheduling lock.

I'm not sure what would be the best way to fix that. One rather easy way
might be to let the scheduling lock pointer point at prv->lock (merging
of the two locks), which is easy doable (credit2 is using a similar scheme
to make the scheduling lock per-runqueue). I'm not sure whether this
wouldn't result in illegal lock nesting (trying to grab prv->lock inside
the scheduling lock), though.

Thoughts?


Juergen

[1]: 
http://logs.test-lab.xenproject.org/osstest/logs/173488/test-armhf-armhf-xl-rtds/serial-cubietruck-picasso.log

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