On Mon, 2018-10-01 at 10:40:39 UTC, "Gautham R. Shenoy" wrote: > From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com> > > Live Partition Migrations require all the present CPUs to execute the > H_JOIN call, and hence rtas_ibm_suspend_me() onlines any offline CPUs > before initiating the migration for this purpose. > > The commit 85a88cabad57 > ("powerpc/pseries: Disable CPU hotplug across migrations") > disables any CPU-hotplug operations once all the offline CPUs are > brought online to prevent any further state change. Once the > CPU-Hotplug operation is disabled, the code assumes that all the CPUs > are online. > > However, there is a minor window in rtas_ibm_suspend_me() between > onlining the offline CPUs and disabling CPU-Hotplug when a concurrent > CPU-offline operations initiated by the userspace can succeed thereby > nullifying the the aformentioned assumption. In this unlikely case > these offlined CPUs will not call H_JOIN, resulting in a system hang. > > Fix this by verifying that all the present CPUs are actually online > after CPU-Hotplug has been disabled, failing which we restore the > state of the offline CPUs in rtas_ibm_suspend_me() and return an > -EBUSY. > > Cc: Nathan Fontenot <nf...@linux.vnet.ibm.com> > Cc: Tyrel Datwyler <tyr...@linux.vnet.ibm.com> > Suggested-by: Michael Ellerman <m...@ellerman.id.au> > Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com> > Reviewed-by: Nathan Fontenot <nf...@linux.vnet.ibm.com>
Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/dfd718a2ed1f678e66749ffe41bdea cheers