[PATCH] migration: Check current_migration in migration_is_running()

[Peter Xu <peterx@redhat.com>]

Report shows that commit 34a8892dec broke iotest 055:

https://lore.kernel.org/r/b8806360-a2b6-4608-83a3-db67e264c733@linaro.org

When replacing migration_is_idle() with "!migration_is_running()", it was
overlooked that the idle helper also checks for current_migration being
available first.

The check would be there if the whole series was applied, but since the
last patches in the previous series rely on some other patches to land
first, we need to recover the behavior of migration_is_idle() first before
that whole set will be merged.

I left migration_is_active / migration_is_device alone, as I don't think
it's possible for them to hit his case (current_migration not initialized).
Also they're prone to removal soon from VFIO side.

Cc: Fabiano Rosas <farosas@suse.de>
Cc: Peter Maydell <peter.maydell@linaro.org>
Fixes: 34a8892dec ("migration: Drop migration_is_idle()")
Reported-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Tested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/migration/migration.c b/migration/migration.c
index aedf7f0751..8c5bd0a75c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1117,6 +1117,10 @@ bool migration_is_running(void)
 {
     MigrationState *s = current_migration;
 
+    if (!s) {
+        return false;
+    }
+
     switch (s->state) {
     case MIGRATION_STATUS_ACTIVE:
     case MIGRATION_STATUS_POSTCOPY_ACTIVE:
-- 
2.45.0