From: Fabiano Rosas <faro...@suse.de>
Fix a segmentation fault in multifd when rb->receivedmap is cleared
too early.
After commit 5ef7e26bdb ("migration/multifd: solve zero page causing
multiple page faults"), multifd started using the rb->receivedmap
bitmap, which belongs to ram.c and is initialized and *freed* from the
ram SaveVMHandlers.
Multifd threads are live until migration_incoming_state_destroy(),
which is called after qemu_loadvm_state_cleanup(), leading to a crash
when accessing rb->receivedmap.
process_incoming_migration_co() ...
qemu_loadvm_state() multifd_nocomp_recv()
qemu_loadvm_state_cleanup() ramblock_recv_bitmap_set_offset()
rb->receivedmap = NULL set_bit_atomic(..., rb->receivedmap)
...
migration_incoming_state_destroy()
multifd_recv_cleanup()
multifd_recv_terminate_threads(NULL)
Move the loadvm cleanup into migration_incoming_state_destroy(), after
multifd_recv_cleanup() to ensure multifd threads have already exited
when rb->receivedmap is cleared.
Adjust the postcopy listen thread comment to indicate that we still
want to skip the cpu synchronization.
CC: qemu-sta...@nongnu.org
Fixes: 5ef7e26bdb ("migration/multifd: solve zero page causing multiple page
faults")
Signed-off-by: Fabiano Rosas <faro...@suse.de>
Link: https://lore.kernel.org/r/20240917185802.15619-3-faro...@suse.de
[peterx: added comment in migration_incoming_state_destroy()]
Signed-off-by: Peter Xu <pet...@redhat.com>
---
migration/migration.c | 5 +++++
migration/savevm.c | 6 ++++--
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/migration/migration.c b/migration/migration.c
index 3dea06d577..ae2be31557 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -378,6 +378,11 @@ void migration_incoming_state_destroy(void)
struct MigrationIncomingState *mis = migration_incoming_get_current();
multifd_recv_cleanup();
+ /*
+ * RAM state cleanup needs to happen after multifd cleanup, because
+ * multifd threads can use some of its states (receivedmap).
+ */
+ qemu_loadvm_state_cleanup();
if (mis->to_src_file) {
/* Tell source that we are done */
diff --git a/migration/savevm.c b/migration/savevm.c
index d0759694fd..7e1e27182a 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2979,7 +2979,10 @@ int qemu_loadvm_state(QEMUFile *f)
trace_qemu_loadvm_state_post_main(ret);
if (mis->have_listen_thread) {
- /* Listen thread still going, can't clean up yet */
+ /*
+ * Postcopy listen thread still going, don't synchronize the
+ * cpus yet.
+ */
return ret;
}
@@ -3022,7 +3025,6 @@ int qemu_loadvm_state(QEMUFile *f)
}
}
- qemu_loadvm_state_cleanup();
cpu_synchronize_all_post_init();
return ret;
--
2.45.0
