Re: [PATCH v4 1/4] migration/savevm.c: reorder usage and assertion of mis->from_src_file

On Wed, 11 Mar 2026 at 18:47, Sergei Heifetz <[email protected]> wrote:
> Reorder the code so the assertion of mis->from_src_file occurs before
> the call to migration_ioc_unregister_yank_from_file, which dereferences
> it in qemu_file_get_ioc.
>
> Fixes: 39675ffffb3394 ("migration: Move the yank unregister of channel_close out")
> Signed-off-by: Sergei Heifetz <[email protected]>
> Reviewed-by: Laurent Vivier <[email protected]>
> ---
>  migration/savevm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 3dc812a7bbb..930a3391e35 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2885,13 +2885,14 @@ static bool postcopy_pause_incoming(MigrationIncomingState *mis)
>
>      assert(migrate_postcopy_ram());
>
> +    assert(mis->from_src_file);
> +
>      /*
>       * Unregister yank with either from/to src would work, since ioc behind it
>       * is the same
>       */
>      migration_ioc_unregister_yank_from_file(mis->from_src_file);
>
> -    assert(mis->from_src_file);
>      qemu_file_shutdown(mis->from_src_file);
>      qemu_fclose(mis->from_src_file);
>      mis->from_src_file = NULL;

*  Change looks okay. But is it really possible that we reach the
Postcopy pause step with mis->from/to_src_file = NULL?
    Maybe we could move the following 'assert(mis->to_src_file);' to
the top too? Make it fail early before any call(s) further.
===
diff --git a/migration/savevm.c b/migration/savevm.c
index 197c89e0e6..18264feaac 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2874,6 +2874,8 @@ static bool
postcopy_pause_incoming(MigrationIncomingState *mis)
     trace_postcopy_pause_incoming();

     assert(migrate_postcopy_ram());
+    assert(mis->from_src_file);
+    assert(mis->to_src_file);

     /*
      * Unregister yank with either from/to src would work, since ioc behind it
@@ -2881,12 +2883,10 @@ static bool
postcopy_pause_incoming(MigrationIncomingState *mis)
      */
     migration_ioc_unregister_yank_from_file(mis->from_src_file);

-    assert(mis->from_src_file);
     qemu_file_shutdown(mis->from_src_file);
     qemu_fclose(mis->from_src_file);
     mis->from_src_file = NULL;

-    assert(mis->to_src_file);
     qemu_file_shutdown(mis->to_src_file);
     qemu_mutex_lock(&mis->rp_mutex);
     qemu_fclose(mis->to_src_file);
===

Thank you.
---
  - Prasad