Hi Peter,
On 2025-08-07 16:57, Peter Xu wrote:
> On Thu, Aug 07, 2025 at 01:49:11PM +0200, Juraj Marcin wrote:
> > From: Juraj Marcin <[email protected]>
> >
> > This patch allows joining the migration listen thread. This is done in
> > preparation for the introduction of "postcopy-setup" state at the
> > beginning of a postcopy migration, when destination can fail gracefully
> > and source side then resume to a running state.
> >
> > In case of such failure, to gracefully perform all cleanup in the main
> > migration thread, we need to wait for the listen thread to exit, which
> > can be done by joining it.
> >
> > Signed-off-by: Juraj Marcin <[email protected]>
> > ---
> > migration/migration.c | 1 +
> > migration/savevm.c | 2 +-
> > 2 files changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index e5ce2940d5..8174e811eb 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -901,6 +901,7 @@ process_incoming_migration_co(void *opaque)
> > * Postcopy was started, cleanup should happen at the end of
> > the
> > * postcopy thread.
> > */
> > + qemu_thread_detach(&mis->listen_thread);
> > trace_process_incoming_migration_co_postcopy_end_main();
> > goto out;
> > }
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index fabbeb296a..d2360be53c 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -2217,7 +2217,7 @@ static int
> > loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
> > mis->have_listen_thread = true;
> > postcopy_thread_create(mis, &mis->listen_thread,
> > MIGRATION_THREAD_DST_LISTEN,
> > - postcopy_ram_listen_thread,
> > QEMU_THREAD_DETACHED);
> > + postcopy_ram_listen_thread,
> > QEMU_THREAD_JOINABLE);
>
> This is good; I actually forgot it used to be detached..
>
> Instead of proactively detach it above, could we always properly join it
However, after the main thread finishes loading device state from the
package, process_incoming_migration_co() exits, and IIUC main thread is
then no longer occupied with migration. So, if we should instead join
the listen thread, we probably should yield the coroutine until the
listen thread can be joined, so we are not blocking the main thread?
> (and hopefully every migration thread)? Then we could drop patch 1 too.
If I haven't missed any, there are no detached migration threads except
listen and get dirty rate threads.
Thanks,
Juraj Marcin
>
> > trace_loadvm_postcopy_handle_listen("return");
> >
> > return 0;
> > --
> > 2.50.1
> >
>
> --
> Peter Xu
>
