Hi Juliet,
Juliet Kim[off-list ref] writes:
Fix extending start/stop topology update scope during LPM
Commit 65b9fdadfc4d ("powerpc/pseries/mobility: Extend start/stop
topology update scope") made the change to the duration that
topology updates are suppressed during LPM to allow the complete
device tree update which leaves the property update notifier
unregistered until device tree update completes. This prevents
topology update during LPM.
Instead, use mutex_lock, which serializes LPM and PRRN operation
in pseries_devicetree_update.
I think this is conflating two issues:
1. Insufficient serialization/ordering of handling PRRNs and
LPM. E.g. we could migrate while processing a PRRN from the source
system and end up with incorrect contents in the device tree on the
destination if the LPM changes the same nodes. The OS is supposed to
drain any outstanding PRRNs before proceeding with migration, which
is a stronger requirement than simple serialization of device tree
updates. If we don't impose this ordering already we should fix that.
2. The NUMA topology update processing. Generally speaking,
start/stop_topology_update() enable/disable dt_update_callback(),
which we use to update CPU-node assignments. Since we now know that
doing that is Bad, it's sort of a happy accident that
migration_store() was changed to re-register the notifier after
updating the device tree, which is too late. So I don't think we
should try to "fix" this. Instead we should remove the broken code
(dt_update_callback -> dlpar_cpu_readdd and so on).
Do you agree?
Thanks,
Nathan