[Qemu-devel] [PATCH] migration: avoid segmentfault when take a snapshot of a VM which being migrated

[jialina01]

During an active background migraion, snapshot will trigger a
segmentfault. As snapshot clears the "current_migration" struct
and updates "to_dst_file" before it finds out that there is a
migration task, Migration accesses the null pointer in
"current_migration" struct and qemu crashes eventually.

Signed-off-by: jialina01 <address@hidden>
Signed-off-by: chaiwen <address@hidden>
Signed-off-by: zhangyu <address@hidden>
---
 migration/savevm.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index 2d10e45582..9cb97ca343 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1319,21 +1319,18 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
     MigrationState *ms = migrate_get_current();
     MigrationStatus status;
 
-    migrate_init(ms);
-
-    ms->to_dst_file = f;
-
     if (migration_is_blocked(errp)) {
-        ret = -EINVAL;
-        goto done;
+        return -EINVAL;
     }
 
     if (migrate_use_block()) {
         error_setg(errp, "Block migration and snapshots are incompatible");
-        ret = -EINVAL;
-        goto done;
+        return -EINVAL;
     }
 
+    migrate_init(ms);
+    ms->to_dst_file = f;
+
     qemu_mutex_unlock_iothread();
     qemu_savevm_state_header(f);
     qemu_savevm_state_setup(f);
@@ -1355,7 +1352,6 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
         error_setg_errno(errp, -ret, "Error while writing VM state");
     }
 
-done:
     if (ret != 0) {
         status = MIGRATION_STATUS_FAILED;
     } else {
-- 
2.13.2.windows.1