Peter Xu <pet...@redhat.com> writes: > On Wed, Nov 08, 2023 at 07:49:53PM -0300, Fabiano Rosas wrote: >> Peter Xu <pet...@redhat.com> writes: >> >> > When a multifd sender thread hit errors, it always needs to kick the main >> > thread by kicking all the semaphores that it can be waiting upon. >> > >> > Provide a helper for it and deduplicate the code. >> > >> > Signed-off-by: Peter Xu <pet...@redhat.com> >> > --- >> > migration/multifd.c | 21 +++++++++++++++------ >> > 1 file changed, 15 insertions(+), 6 deletions(-) >> > >> > diff --git a/migration/multifd.c b/migration/multifd.c >> > index 4afdd88602..33fb21d0e4 100644 >> > --- a/migration/multifd.c >> > +++ b/migration/multifd.c >> > @@ -374,6 +374,18 @@ struct { >> > MultiFDMethods *ops; >> > } *multifd_send_state; >> > >> > +/* >> > + * The migration thread can wait on either of the two semaphores. This >> > + * function can be used to kick the main thread out of waiting on either >> > of >> > + * them. Should mostly only be called when something wrong happened with >> > + * the current multifd send thread. >> > + */ >> > +static void multifd_send_kick_main(MultiFDSendParams *p) >> > +{ >> > + qemu_sem_post(&p->sem_sync); >> > + qemu_sem_post(&multifd_send_state->channels_ready); >> > +} >> > + >> > /* >> > * How we use multifd_send_state->pages and channel->pages? >> > * >> > @@ -746,8 +758,7 @@ out: >> > assert(local_err); >> > trace_multifd_send_error(p->id); >> > multifd_send_terminate_threads(local_err); >> > - qemu_sem_post(&p->sem_sync); >> > - qemu_sem_post(&multifd_send_state->channels_ready); >> > + multifd_send_kick_main(p); >> > error_free(local_err); >> > } >> > >> > @@ -787,8 +798,7 @@ static void multifd_tls_outgoing_handshake(QIOTask >> > *task, >> > * is not created, and then tell who pay attention to me. >> > */ >> > p->quit = true; >> > - qemu_sem_post(&multifd_send_state->channels_ready); >> > - qemu_sem_post(&p->sem_sync); >> > + multifd_send_kick_main(p); >> >> There's a bug here in the original code: >> >> It's not really safe to call any of these outside of the channel lock >> because multifd_save_cleanup() could execute at the same time and call >> qemu_sem_destroy() -> qemu_mutex_destroy(), which can assert because we >> might be holding the sem_lock. > > If you meant "p->mutex" as the "channel lock", IIUC even holding that won't > work? Because it'll also be freed in multifd_save_cleanup(). >
You're right, I just sent an RFC about this, please take a look.