Re: [PATCH 2/2] migration: Fix return-path thread exit

[Cédric Le Goater]

On 2/2/24 15:42, Fabiano Rosas wrote:
> Cédric Le Goater <clg@redhat.com> writes:
>
> > In case of error, close_return_path_on_source() can perform a shutdown
> > to exit the return-path thread.  However, in migrate_fd_cleanup(),
> > 'to_dst_file' is closed before calling close_return_path_on_source()
> > and the shutdown fails, leaving the source and destination waiting for
> > an event to occur.
>
> At close_return_path_on_source, qemu_file_shutdown() and checking
> ms->to_dst_file are done under the qemu_file_lock, so how could
> migrate_fd_cleanup() have cleared the pointer but the ms->to_dst_file
> check have passed?

This is not a locking issue, it's much simpler. migrate_fd_cleanup()
clears the ms->to_dst_file pointer and closes the QEMUFile and then
calls close_return_path_on_source() which then tries to use resources
which are not available anymore.

Thanks,

C.




> > Close the file after calling close_return_path_on_source() so that the
> > shutdown succeeds and the return-path thread exits.
> >
> > Signed-off-by: Cédric Le Goater <clg@redhat.com>
> > ---
> >   migration/migration.c | 12 +++++-------
> >   1 file changed, 5 insertions(+), 7 deletions(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 
> > 2c3362235c7651c11d581f3c3639571f1f9636ef..1e0b6acaedc272e8ce26ad40be2c42177f5fd14e
> >  100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1314,6 +1314,7 @@ void migrate_set_state(int *state, int old_state, int 
> > new_state)
> >   static void migrate_fd_cleanup(MigrationState *s)
> >   {
> >       int file_error = 0;
> > +    QEMUFile *tmp = NULL;
> >   
> >       g_free(s->hostname);
> >       s->hostname = NULL;
> > @@ -1323,8 +1324,6 @@ static void migrate_fd_cleanup(MigrationState *s)
> >       qemu_savevm_state_cleanup();
> >   
> >       if (s->to_dst_file) {
> > -        QEMUFile *tmp;
> > -
> >           trace_migrate_fd_cleanup();
> >           bql_unlock();
> >           if (s->migration_thread_running) {
> > @@ -1344,15 +1343,14 @@ static void migrate_fd_cleanup(MigrationState *s)
> >            * critical section won't block for long.
> >            */
> >           migration_ioc_unregister_yank_from_file(tmp);
> > -        qemu_fclose(tmp);
> >       }
> >   
> > -    /*
> > -     * We already cleaned up to_dst_file, so errors from the return
> > -     * path might be due to that, ignore them.
> > -     */
> >       close_return_path_on_source(s, file_error);
> >   
> > +    if (tmp) {
> > +        qemu_fclose(tmp);
> > +    }
> > +
> >       assert(!migration_is_active(s));
> >   
> >       if (s->state == MIGRATION_STATUS_CANCELLING) {