* Peter Xu (pet...@redhat.com) wrote:
> Logically below race could trigger with the old code:
>
> test program migration thread
> ------------ ----------------
> wait_until('postcopy-pause')
> postcopy_pause()
> set_state('postcopy-pause')
> do_postcopy_recover()
> arm s->to_dst_file with new fd
> release s->to_dst_file [1]
>
> Here [1] could have released the just-installed recoverying channel. Then the
> migration could hang without really resuming.
>
> Instead, it should be very safe to release the fd before setting the state
> into
> 'postcopy-pause', because there's no reason for any other thread to touch it
> during 'postcopy-active'.
>
> Dave reported a very rare postcopy recovery hang that the migration-test
> program waited for the migration to complete in migrate_postcopy_complete().
> We do suspect it's the same thing that we're gonna fix here. Hard to tell.
> However since we've noticed this, fix this irrelevant of the hang report.
>
> Cc: Dr. David Alan Gilbert <dgilb...@redhat.com>
> Cc: Juan Quintela <quint...@redhat.com>
> Signed-off-by: Peter Xu <pet...@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> migration/migration.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 0b4fcff01f..50df6251b7 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -3182,9 +3182,6 @@ static MigThrError postcopy_pause(MigrationState *s)
> while (true) {
> QEMUFile *file;
>
> - migrate_set_state(&s->state, s->state,
> - MIGRATION_STATUS_POSTCOPY_PAUSED);
> -
> /* Current channel is possibly broken. Release it. */
> assert(s->to_dst_file);
> qemu_mutex_lock(&s->qemu_file_lock);
> @@ -3195,6 +3192,9 @@ static MigThrError postcopy_pause(MigrationState *s)
> qemu_file_shutdown(file);
> qemu_fclose(file);
>
> + migrate_set_state(&s->state, s->state,
> + MIGRATION_STATUS_POSTCOPY_PAUSED);
> +
> error_report("Detected IO failure for postcopy. "
> "Migration paused.");
>
> --
> 2.26.2
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
