When a send thread encounters an error (as is the case with yank), it sets multifd_send_state->exiting and the other threads exit too. This races with multifd_send_sync_main() which now hangs at qemu_sem_wait(&p->sem_sync) in multifd_send_sync_main() line 647 as it waits for threads that have exited.
Fix this by kicking the semaphores when exiting the send threads. I encountered this hang when stress testing the colo unit test, though I was unable to write a migration test to reliably hit this. Reviewed-by: Peter Xu <[email protected]> Signed-off-by: Lukas Straub <[email protected]> --- migration/multifd.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/migration/multifd.c b/migration/multifd.c index 220ed8564960fdabc58e4baa069dd252c8ad293c..7762aab8e0702672d3730f27e9c9ee3b86500f0c 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -772,9 +772,14 @@ out: assert(local_err); trace_multifd_send_error(p->id); multifd_send_error_propagate(local_err); - multifd_send_kick_main(p); } + /* + * Always kick the main thread: The main thread might wait on this thread + * while another thread encounters an error and signals this thread to exit. + */ + multifd_send_kick_main(p); + rcu_unregister_thread(); trace_multifd_send_thread_end(p->id, p->packets_sent); -- 2.39.5
