On 09/29/2015 08:13 AM, Amit Shah wrote:
There have been multiple versions of this patch on the list, can you
please annotate that this is v3 so it supersedes the earlier v2?
Also, please include a changelog in the description in patch 0 so we
know what happened between the various versions.
Thanks,
On (Mon) 28 Sep 2015 [14:41:58], 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
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>
---
migration/ram.c | 44 +++++++++++++++++++++++++++-----------------
1 file changed, 27 insertions(+), 17 deletions(-)
Amit
this one is correct. I am sorry, I have missed v3 here in the subject.
Den
