Re: [PATCH v3 0/2] migration/tls: Graceful shutdowns for main and postcopy channels

[Peter Xu <peterx@redhat.com>]

On Thu, Sep 18, 2025 at 06:17:37PM -0300, Fabiano Rosas wrote:
> > ============= ABOUT OLD PATCH 2 ===================
> >
> > I dropped it for now to unblock almost patch 1, because patch 1 will fix a
> > real warning that can be triggered for not only qtest but also normal tls
> > postcopy migration.
> >
> > While I was looking at temporary settings for multifd send iochannels to be
> > blocking always, I found I cannot explain how migration_tls_channel_end()
> > currently works, because it writes to the multifd iochannels while the
> > channels should still be owned (and can be written at the same time?) by
> > the sender threads.  It sounds like a thread-safety issue, or is it not?
> >
> 
> IIUC, the multifd channels will be stuck at p->sem because this is the
> success path so migration will have already finished when we reach
> migration_cleanup(). The ram/device state migration will hold the main
> thread until the multifd channels finish transferring.

For success cases, indeed.  However this is not the success path?  After
all, we check migration_has_failed().

Should I then send a patch to only send bye() when succeeded?  Then I can
also add some comment.  I wished we could assert.  Then the "temporarily
changing nonblock mode" will also rely on this one, because ideally we
shouldn't touch the fd nonblocking mode if some other thread is operating
on it.

The other thing is I also think we shouldn't rely on checking
"p->tls_thread_created && p->thread_created" but only rely on channel type,
which might be more straightforward (I almost did it in v1, but v2 rewrote
things so it was lost).

-- 
Peter Xu