On 13/03/2020 11:23, Jan Beulich wrote: > On 10.03.2020 19:06, Igor Druzhinin wrote: >> During CPU down operation RCU callbacks are scheduled to finish >> off some actions later as soon as CPU is fully dead (the same applies >> to CPU up operation in case error path is taken). If in the same grace >> period another CPU up operation is performed on the same CPU, RCU callback >> will be called later on a CPU in a potentially wrong (already up again >> instead of still being down) state leading to eventual state inconsistency >> and/or crash. >> >> In order to avoid it - flush RCU callbacks explicitly before starting the >> next CPU up/down operation. >> >> Reviewed-by: Juergen Gross <jgr...@suse.com> >> Signed-off-by: Igor Druzhinin <igor.druzhi...@citrix.com> >> --- >> This got discovered trying to resume PV shim with multiple vCPUs on AMD >> machine (where park_offline_cpus == 0). RCU callback responsible for >> freeing percpu area on CPU offline got finally called after CPU went >> online again as the guest performed regular vCPU offline/online operations >> on resume. >> >> Note: this patch requires RCU series v4 from Juergen to be applied - >> https://lists.xenproject.org/archives/html/xen-devel/2020-03/msg00668.html > > I was about to apply the patch yesterday (I think) when I stumbled > across this note. Is this actually still true? If so, would you > mind helping me see the dependency?
Yes, that's the case otherwise you're risking to crash near 100% of installations as rcu_barrirer without Juergen's fixes is simply broken. Igor _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
