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.
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(-)
--
2.1.4
