From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7AA98C2A09B for ; Fri, 7 Aug 2026 13:41:27 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wsKox-0006Xb-B3; Fri, 07 Aug 2026 09:41:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wsKov-0006X3-KI for qemu-devel@nongnu.org; Fri, 07 Aug 2026 09:41:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wsKot-0002yV-UI for qemu-devel@nongnu.org; Fri, 07 Aug 2026 09:41:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1786110067; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UUf7ST3t0GG6c4E8ye9mGEz9ifzwyqaEOtooB/hZTi8=; b=SRbG8XzCw/gk3/9uRpQxAt5jxSGkZtyiy+FWrG+L9N6CfjOGJsyk8zCMjaHzGdmOSRSFzU N1E/uugruU0HRFHgxM5z+zdeplbFT8+NeZCVvUNXoxQ2i9o1mWBcfoXsqnVHXsDj+TwWzd mMWGrjVYJJuvbWAJIWoW0lOwr+/D6rc= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-284-uxc3fgn_POeQABlhDZStVA-1; Fri, 07 Aug 2026 09:41:06 -0400 X-MC-Unique: uxc3fgn_POeQABlhDZStVA-1 X-Mimecast-MFC-AGG-ID: uxc3fgn_POeQABlhDZStVA_1786110065 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2900C1956041; Fri, 7 Aug 2026 13:41:05 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.7]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 843AE180049F; Fri, 7 Aug 2026 13:41:04 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 3C14321E6920; Fri, 07 Aug 2026 15:41:02 +0200 (CEST) From: Markus Armbruster To: Zhang Chen Cc: qemu-devel , Eric Blake , "Michael S . Tsirkin" , Stefan Hajnoczi , Paolo Bonzini , 'Daniel P . =?utf-8?Q?Berrang=C3=A9'?= , Jason Wang Subject: Re: [PATCH V11 03/15] iothread: track users with holder name In-Reply-To: <20260806202531.243806-4-zhangckid@gmail.com> (Zhang Chen's message of "Fri, 7 Aug 2026 04:25:12 +0800") References: <20260806202531.243806-1-zhangckid@gmail.com> <20260806202531.243806-4-zhangckid@gmail.com> Date: Fri, 07 Aug 2026 15:41:02 +0200 Message-ID: <87wlu2nj4h.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 0 X-Spam_score: -0.0 X-Spam_bar: / X-Spam_report: (-0.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.238, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Zhang Chen 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 > --- > 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. > +{ > + /* Delete IOThreadHolder from the list */ > + iothread_unref(iothread, holder); > +} > + > static int query_one_iothread(Object *object, void *opaque) > { > IOThreadInfoList ***tail = opaque;