On 09/25/2015 05:09 PM, Denis V. Lunev 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 > > Patches here are quick and dirty, compile-tested only to validate the > architectual approach. > > Igor, Anna, can you pls start your tests with these patches instead of your > original one. Thank you.
Can you give me the backtrace of the working thread? I think it is very bad to wait some lock in rcu reader's cirtical section. To Paolo: Do we allow this in rcu critical section? Thanks Wen Congyang > > Signed-off-by: Denis V. Lunev <d...@openvz.org> > CC: Igor Redko <red...@virtuozzo.com> > CC: Anna Melekhova <an...@virtuozzo.com> > CC: Juan Quintela <quint...@redhat.com> > CC: Amit Shah <amit.s...@redhat.com> > > Denis V. Lunev (2): > migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0 > migration: fix deadlock > > migration/ram.c | 45 ++++++++++++++++++++++++++++----------------- > 1 file changed, 28 insertions(+), 17 deletions(-) >
