On Wed, Aug 12, 2026 at 3:19 AM Stefan Hajnoczi <[email protected]> wrote:
>
> On Tue, Aug 11, 2026 at 04:51:55PM +0800, Zhang Chen wrote:
> > On Fri, Aug 7, 2026 at 9:41 PM Markus Armbruster <[email protected]> wrote:
> > >
> > > Zhang Chen <[email protected]> writes:
> > >
> > > > Introduce iothread_ref_and_get_aio_context() with a holder argument
> > > > and its counterpart iothread_put_aio_context().
> > > >
> > > > Previously, users of an IOThread AioContext did not explicitly record
> > > > their identity, making it difficult to debug which devices or
> > > > subsystems were pinning an IOThread.
> > > >
> > > > Registering a holder takes an IOThread object reference so that the
> > > > IOThread and its AioContext stay alive until the matching put
> > > > operation. Document the ownership and BQL requirements.
> > > >
> > > > Signed-off-by: Zhang Chen <[email protected]>
> > > > ---
> > > > include/system/iothread.h | 21 +++++++++++++++++++++
> > > > iothread.c | 23 ++++++++++++++++++++++-
> > > > 2 files changed, 43 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/include/system/iothread.h b/include/system/iothread.h
> > > > index b8aeb32b0e..b6664e7a38 100644
> > > > --- a/include/system/iothread.h
> > > > +++ b/include/system/iothread.h
> > > > @@ -67,6 +67,27 @@ DECLARE_INSTANCE_CHECKER(IOThread, IOTHREAD,
> > > > char *iothread_get_id(IOThread *iothread);
> > > > IOThread *iothread_by_id(const char *id);
> > > > AioContext *iothread_get_aio_context(IOThread *iothread);
> > > > +
> > > > +/*
> > > > + * Register @holder and return @iothread's AioContext. The holder is
> > > > copied,
> > > > + * and a reference is taken on @iothread so that both the IOThread and
> > > > its
> > > > + * AioContext remain alive.
> > > > + *
> > > > + * The caller must eventually call iothread_put_aio_context() with an
> > > > + * equivalent holder. This function is not thread-safe and must be
> > > > called
> > > > + * under the Big QEMU Lock (BQL).
> > > > + */
> > > > +AioContext *iothread_ref_and_get_aio_context(IOThread *iothread,
> > > > + const IOThreadHolder
> > > > *holder);
> > > > +
> > > > +/*
> > > > + * Unregister @holder and release the corresponding reference on
> > > > @iothread.
> > > > + * Calling this function without a matching
> > > > + * iothread_ref_and_get_aio_context() call is a programming error.
> > > > + *
> > > > + * This function is not thread-safe and must be called under the BQL.
> > > > + */
> > > > +void iothread_put_aio_context(IOThread *iothread, const IOThreadHolder
> > > > *holder);
> > > > GMainContext *iothread_get_g_main_context(IOThread *iothread);
> > > >
> > > > /*
> > > > diff --git a/iothread.c b/iothread.c
> > > > index 2a4c92e08b..0cc8344ee6 100644
> > > > --- a/iothread.c
> > > > +++ b/iothread.c
> > > > @@ -33,6 +33,11 @@ void iothread_ref(IOThread *iothread, const
> > > > IOThreadHolder *holder)
> > > > assert(holder);
> > > >
> > > > QAPI_LIST_PREPEND(iothread->holders, QAPI_CLONE(IOThreadHolder,
> > > > holder));
> > > > + /*
> > > > + * This guarantees that the IOThread and its AioContext remain
> > > > alive
> > > > + * as long as there is a holder.
> > > > + */
> > > > + object_ref(OBJECT(iothread));
> > > > }
> > > >
> > > > static int iothread_holder_compare(const IOThreadHolder *holder_a,
> > > > @@ -78,6 +83,7 @@ void iothread_unref(IOThread *iothread, const
> > > > IOThreadHolder *holder)
> > > > *prev = curr->next;
> > > > curr->next = NULL;
> > > > qapi_free_IOThreadHolderList(curr);
> > > > + object_unref(OBJECT(iothread));
> > > > return;
> > > > }
> > > > prev = &curr->next;
> > > > @@ -199,7 +205,7 @@ static void iothread_init_gcontext(IOThread
> > > > *iothread, const char *thread_name)
> > > > g_autofree char *name = g_strdup_printf("%s aio-context",
> > > > thread_name);
> > > >
> > > > iothread->worker_context = g_main_context_new();
> > > > - source = aio_get_g_source(iothread_get_aio_context(iothread));
> > > > + source = aio_get_g_source(iothread->ctx);
> > > > g_source_set_name(source, name);
> > > > g_source_attach(source, iothread->worker_context);
> > > > g_source_unref(source);
> > > > @@ -421,6 +427,21 @@ AioContext *iothread_get_aio_context(IOThread
> > > > *iothread)
> > > > return iothread->ctx;
> > > > }
> > > >
> > > > +AioContext *iothread_ref_and_get_aio_context(IOThread *iothread,
> > > > + const IOThreadHolder
> > > > *holder)
> > > > +{
> > > > + /* Add IOThreadHolder to the list */
> > > > + iothread_ref(iothread, holder);
> > > > +
> > > > + return iothread->ctx;
> > > > +}
> > > > +
> > > > +void iothread_put_aio_context(IOThread *iothread, const IOThreadHolder
> > > > *holder)
> > >
> > > Should we name this "unref" rather than "put"? Perhaps Stefan has an
> > > opinion.
> >
> > It's OK for me. The original code was designed to match the
> > "iothread_get_aio_context",
> > If Stefan has no objection， I will change the name to
> > "iothread_unref_aio_context".
>
> iothread_unref_and_put_aio_context() would be consistent with
> iothread_ref_and_get_aio_context() :)
Sure, it looks much better.
Thanks
Chen
>
> Stefan
>
> >
> > Thanks
> >
> > Chen
> >
> > >
> > > > +{
> > > > + /* Delete IOThreadHolder from the list */
> > > > + iothread_unref(iothread, holder);
> > > > +}
> > > > +
> > > > static int query_one_iothread(Object *object, void *opaque)
> > > > {
> > > > IOThreadInfoList ***tail = opaque;
> > >
> >
