From patchwork Mon May 6 19:06:22 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13655910 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 lists.gnu.org (lists.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 F1035C25B74 for ; Mon, 6 May 2024 19:07:24 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1s43fp-00030P-Po; Mon, 06 May 2024 15:06:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1s43fa-0002rV-6b for qemu-devel@nongnu.org; Mon, 06 May 2024 15:06:40 -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 1s43fY-0000B9-FS for qemu-devel@nongnu.org; Mon, 06 May 2024 15:06:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1715022395; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EaNV6j44T8hFyYd9mWj4JUcAH/rY+FTEpab1tHrtqVI=; b=HSeIZAkZ4thSb/KP7ySP5JIoVIj71yHHyqiGoMCJYFq5vs7GA0BpQJf34i3FE9L1ghuYbg xvwX/IwY+PUt034e+GdlpVutynVPzpL9DWHSAOvFcfITAOf2ueTykX4HxaOaVl5UDMQ1f/ DOVQtHMXl+6P1erA0NPm1+69OMkMj/Y= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-586-rbqpOyRaMq6o3k0wNx0F8A-1; Mon, 06 May 2024 15:06:31 -0400 X-MC-Unique: rbqpOyRaMq6o3k0wNx0F8A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2F65818065AB; Mon, 6 May 2024 19:06:31 +0000 (UTC) Received: from localhost (unknown [10.39.192.54]) by smtp.corp.redhat.com (Postfix) with ESMTP id 568DB40C6DAE; Mon, 6 May 2024 19:06:30 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Markus Armbruster , Michael Roth , Kevin Wolf , Hanna Czenczek , Stefan Hajnoczi , qemu-block@nongnu.org, Fam Zheng Subject: [PATCH 2/2] aio: warn about iohandler_ctx special casing Date: Mon, 6 May 2024 15:06:22 -0400 Message-ID: <20240506190622.56095-3-stefanha@redhat.com> In-Reply-To: <20240506190622.56095-1-stefanha@redhat.com> References: <20240506190622.56095-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.581, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: 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 The main loop has two AioContexts: qemu_aio_context and iohandler_ctx. The main loop runs them both, but nested aio_poll() calls on qemu_aio_context exclude iohandler_ctx. Which one should qemu_get_current_aio_context() return when called from the main loop? Document that it's always qemu_aio_context. This has subtle effects on functions that use qemu_get_current_aio_context(). For example, aio_co_reschedule_self() does not work when moving from iohandler_ctx to qemu_aio_context because qemu_get_current_aio_context() does not differentiate these two AioContexts. Document this in order to reduce the chance of future bugs. Signed-off-by: Stefan Hajnoczi --- include/block/aio.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/block/aio.h b/include/block/aio.h index 8378553eb9..4ee81936ed 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -629,6 +629,9 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co); * * Move the currently running coroutine to new_ctx. If the coroutine is already * running in new_ctx, do nothing. + * + * Note that this function cannot reschedule from iohandler_ctx to + * qemu_aio_context. */ void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx); @@ -661,6 +664,9 @@ void aio_co_enter(AioContext *ctx, Coroutine *co); * If called from an IOThread this will be the IOThread's AioContext. If * called from the main thread or with the "big QEMU lock" taken it * will be the main loop AioContext. + * + * Note that the return value is never the main loop's iohandler_ctx and the + * return value is the main loop AioContext instead. */ AioContext *qemu_get_current_aio_context(void);