Introduce iothread_ref_and_get_aio_context() with a holder argument and its counterpart iothread_unref_and_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 | 22 ++++++++++++++++++++++ iothread.c | 24 +++++++++++++++++++++++- 2 files changed, 45 insertions(+), 1 deletion(-) diff --git a/include/system/iothread.h b/include/system/iothread.h index b8aeb32b0e..f6c5f95dd9 100644 --- a/include/system/iothread.h +++ b/include/system/iothread.h @@ -67,6 +67,28 @@ 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_unref_and_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_unref_and_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..64be852d1c 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 +427,22 @@ 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_unref_and_put_aio_context(IOThread *iothread, + const IOThreadHolder *holder) +{ + /* Delete IOThreadHolder from the list */ + iothread_unref(iothread, holder); +} + static int query_one_iothread(Object *object, void *opaque) { IOThreadInfoList ***tail = opaque; -- 2.54.0
