"Denis V. Lunev" <d...@openvz.org> wrote: > Release qemu global mutex before call synchronize_rcu(). > synchronize_rcu() waiting for all readers to finish their critical > sections. There is at least one critical section in which we try > to get QGM (critical section is in address_space_rw() and > prepare_mmio_access() is trying to aquire QGM). > > Both functions (migration_end() and migration_bitmap_extend()) > are called from main thread which is holding QGM. > > Thus there is a race condition that ends up with deadlock: > main thread working thread > Lock QGA | > | Call KVM_EXIT_IO handler > | | > | Open rcu reader's critical section > Migration cleanup bh | > | | > synchronize_rcu() is | > waiting for readers | > | prepare_mmio_access() is waiting for QGM > \ / > deadlock > > The patch changes bitmap freeing from direct g_free after synchronize_rcu > to free inside call_rcu. > > Signed-off-by: Denis V. Lunev <d...@openvz.org> > Reported-by: Igor Redko <red...@virtuozzo.com> > Tested-by: Igor Redko <red...@virtuozzo.com> > CC: Anna Melekhova <an...@virtuozzo.com> > CC: Juan Quintela <quint...@redhat.com> > CC: Amit Shah <amit.s...@redhat.com> > CC: Paolo Bonzini <pbonz...@redhat.com> > CC: Wen Congyang <we...@cn.fujitsu.com>
Reviewed-by: Juan Quintela <quint...@redhat.com> Appliefd to my tree. PD, no I still don't understood how RCU gave us so many corner cases wrong.
