From nobody Thu Apr 2 15:39:38 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=quarantine dis=none) header.from=bytedance.com ARC-Seal: i=1; a=rsa-sha256; t=1774617098; cv=none; d=zohomail.com; s=zohoarc; b=dlq8CMjbjH0jTXVD8eAf+sYDUwMXg0/QfxFKlNXRsRNzF2szFFTlpyvivc+tJ11Ugb3hRsVGzxgsbM3or6a2fdOO6uXUfy5xtE7ySCl6t40hI1I4FtzTidVpCpS/XHd2JtwjIULEDTDWd7goMXLq0EppoPkg28T65rFUxWxub4s= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1774617098; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=l/lgnMIV8DNoZCBSRTWY7xYrOxj5DgN3eWBfLFhjboU=; b=PxfZAtlaZnssc/Kk2C3pZ5HKpGtotVrVsRaNRh+ni7Tg347Za5upayD2/4hU45bQX64FMyGMgLVGUpwXtlMpkL1WUwUXWzzYeY+9OVVpG+F75Yv+UWdKNfcIUGZ8531Fyei1YEMratn5UCCA06ihcMuEpIwBanrplBd34HSasII= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass header.from= (p=quarantine dis=none) Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1774617098213299.2616676843679; Fri, 27 Mar 2026 06:11:38 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w66xr-0000ph-WA; Fri, 27 Mar 2026 09:11:04 -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 1w66xo-0000pY-Ue for qemu-devel@nongnu.org; Fri, 27 Mar 2026 09:11:01 -0400 Received: from va-1-111.ptr.blmpb.com ([209.127.230.111]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1w66xm-0005zZ-0o for qemu-devel@nongnu.org; Fri, 27 Mar 2026 09:11:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1774617040; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=l/lgnMIV8DNoZCBSRTWY7xYrOxj5DgN3eWBfLFhjboU=; b=jfcNvF8tFlaYJ1nkitWy70Ksy9cV2OqJRFntlKCrttASDwgPUYNQUlz88np3agWqK5mctP xJ6vD1oZRbgDNN01SsrQUvcwyWOmD8YkjZYiNXZKICHH3ECkO+f6EYU8f/a/k6pWX6CTrP VsC58JKx2k3aH/fpIPsxwCCLuysGdGZd/6M2A4YDWK5X8yL5CgMi/+/a0gtyPuSMBsXNG7 kx1NuxSsnFF+6xygoGjK+nTS9Cr7KJ2JQnwTe306CVamsSyUqudhdlyzS9GDzpvCQUi2PP wkjdvp6Qt/0aaaMlUMOjVygMzfJYXUxr4IluzjsIMcdnLmAXjA5PrdoMZDn8lw== Date: Fri, 27 Mar 2026 21:10:24 +0800 X-Mailer: git-send-email 2.32.1 (Apple Git-133) To: Cc: , , , , "hongmianquan" Message-Id: <20260327131024.51947-1-hongmianquan@bytedance.com> Mime-Version: 1.0 X-Original-From: hongmianquan X-Lms-Return-Path: From: "hongmianquan" Subject: [PATCH v2] monitor: Fix deadlock in monitor_cleanup Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=209.127.230.111; envelope-from=hongmianquan@bytedance.com; helo=va-1-111.ptr.blmpb.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @bytedance.com) X-ZM-MESSAGEID: 1774617101575158500 Content-Type: text/plain; charset="utf-8" During qemu_cleanup, if a non-coroutine QMP command (e.g., query-commands) = is concurrently received and processed by the mon_iothread, it can lead to a deadlock in mo= nitor_cleanup. The root cause is a race condition between the main thread's shutdown seque= nce and the coroutine's dispatching mechanism. When handling a non-coroutin= e QMP command, qmp_dispatcher_co schedules the actual command execution as = a bottom half in iohandler_ctx and then yields. At this suspended point, qm= p_dispatcher_co_busy remains true. Subsequently, the main thread in monitor_cleanup(), sets qmp_dispatcher_co_= shutdown, and calls qmp_dispatcher_co_wake(). Since qmp_dispatcher_co_busy = is already true, the aio_co_wake is skipped. The main thread then enters th= e AIO_WAIT_WHILE_UNLOCKED loop, it executes the scheduled BH (do_qmp_dispat= ch_bh) via aio_poll(iohandler_ctx, false), which attempts to wake up the co= routine, aio_co_wake schedules a new wake-up BH in iohandler_ctx. The main = thread then blocks indefinitely in aio_poll(qemu_aio_context, true), while = the coroutine's wake-up BH is starved in iohandler_ctx, qmp_dispatcher_co n= ever reaches termination, resulting in a deadlock. The execution sequence is illustrated below: IO Thread Main Thread (qemu_aio_context) qmp_dispat= cher_co (iohandler_ctx) | | = | |-- query-commands | = | |-- qmp_dispatcher_co_wake() | = | | (sets busy =3D true) | = | | | <-- Wakes up in iohandler_ctx -->= | | | = |-- qmp_dispatch() | | = |-- Schedules BH (do_qmp_dispatch_bh) | | = |-- qemu_coroutine_yield() | | = [State: Suspended, busy=3Dtrue] | [ quit triggered ] | | |-- monitor_cleanup() | |-- qmp_dispatcher_co_shutdown =3D tr= ue | |-- qmp_dispatcher_co_wake() | | -> Checks busy flag. It's TRUE! | | -> Skips aio_co_wake(). | | | |-- AIO_WAIT_WHILE_UNLOCKED: | | |-- aio_poll(iohandler_ctx, false) | | | -> Executes do_qmp_dispatch_= bh | | | -> Schedules 'co_schedule_bh= ' in iohandler_ctx | | | | | |-- aio_poll(qemu_aio_context, tr= ue) | | | -> Blocks indefinitely! (Dea= dlock) | | | X (Main thread sleeping) = X (Waiting for next iohandler_ctx poll) To fix this, we add an explicit aio_wait_kick() in do_qmp_dispatch_bh() to = break the main loop out of its blocking poll, allowing it to evaluate the l= oop condition and poll iohandler_ctx. Signed-off-by: hongmianquan Signed-off-by: wubo.bob Acked-by: Markus Armbruster Suggested-by: Kevin Wolf --- qapi/qmp-dispatch.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c index 9bb1e6a9f4..e3897d5197 100644 --- a/qapi/qmp-dispatch.c +++ b/qapi/qmp-dispatch.c @@ -128,6 +128,16 @@ static void do_qmp_dispatch_bh(void *opaque) data->cmd->fn(data->args, data->ret, data->errp); monitor_set_cur(qemu_coroutine_self(), NULL); aio_co_wake(data->co); + + /* + * If the QMP dispatcher coroutine is waiting to be scheduled + * in iohandler_ctx, we must kick the main loop. This ensures + * that AIO_WAIT_WHILE_UNLOCKED() in monitor_cleanup() doesn't + * block indefinitely waiting for an event in qemu_aio_context, + * but actually gets the chance to poll iohandler_ctx and resume + * the coroutine. + */ + aio_wait_kick(); } =20 /* --=20 2.32.1 (Apple Git-133)