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Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; Received: from SATLEXMB04.amd.com (165.204.84.17) by DM6NAM11FT018.mail.protection.outlook.com (10.13.172.110) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.4608.15 via Frontend Transport; Tue, 19 Oct 2021 14:31:07 +0000 Received: from localhost (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Tue, 19 Oct 2021 09:31:07 -0500 From: Michael Roth To: CC: , Stefan Reiter , Wolfgang Bumiller , Kevin Wolf , Markus Armbruster Subject: [PATCH 04/64] monitor/qmp: fix race on CHR_EVENT_CLOSED without OOB Date: Tue, 19 Oct 2021 09:08:44 -0500 Message-ID: <20211019140944.152419-5-michael.roth@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211019140944.152419-1-michael.roth@amd.com> References: <20211019140944.152419-1-michael.roth@amd.com> MIME-Version: 1.0 X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: e5da0cc0-774f-4594-f876-08d9930d16e4 X-MS-TrafficTypeDiagnostic: PH0PR12MB5465: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:357; 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envelope-from=Michael.Roth@amd.com; helo=NAM04-DM6-obe.outbound.protection.outlook.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_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-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: 2.1.23 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" From: Stefan Reiter The QMP dispatcher coroutine holds the qmp_queue_lock over a yield point, where it expects to be rescheduled from the main context. If a CHR_EVENT_CLOSED event is received just then, it can race and block the main thread on the mutex in monitor_qmp_cleanup_queue_and_resume. monitor_resume does not need to be called from main context, so we can call it immediately after popping a request from the queue, which allows us to drop the qmp_queue_lock mutex before yielding. Suggested-by: Wolfgang Bumiller Signed-off-by: Stefan Reiter Message-Id: <20210322154024.15011-1-s.reiter@proxmox.com> Reviewed-by: Kevin Wolf Cc: qemu-stable@nongnu.org Signed-off-by: Markus Armbruster (cherry picked from commit a67b996e7894edfafbcd3fd007c9f58f26d25908) Signed-off-by: Michael Roth --- monitor/qmp.c | 40 ++++++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 18 deletions(-) diff --git a/monitor/qmp.c b/monitor/qmp.c index 2b0308f933..092c527b6f 100644 --- a/monitor/qmp.c +++ b/monitor/qmp.c @@ -257,24 +257,6 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data) trace_monitor_qmp_in_band_dequeue(req_obj, req_obj->mon->qmp_requests->length); - if (qatomic_xchg(&qmp_dispatcher_co_busy, true) == true) { - /* - * Someone rescheduled us (probably because a new requests - * came in), but we didn't actually yield. Do that now, - * only to be immediately reentered and removed from the - * list of scheduled coroutines. - */ - qemu_coroutine_yield(); - } - - /* - * Move the coroutine from iohandler_ctx to qemu_aio_context for - * executing the command handler so that it can make progress if it - * involves an AIO_WAIT_WHILE(). - */ - aio_co_schedule(qemu_get_aio_context(), qmp_dispatcher_co); - qemu_coroutine_yield(); - /* * @req_obj has a request, we hold req_obj->mon->qmp_queue_lock */ @@ -298,8 +280,30 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data) monitor_resume(&mon->common); } + /* + * Drop the queue mutex now, before yielding, otherwise we might + * deadlock if the main thread tries to lock it. + */ qemu_mutex_unlock(&mon->qmp_queue_lock); + if (qatomic_xchg(&qmp_dispatcher_co_busy, true) == true) { + /* + * Someone rescheduled us (probably because a new requests + * came in), but we didn't actually yield. Do that now, + * only to be immediately reentered and removed from the + * list of scheduled coroutines. + */ + qemu_coroutine_yield(); + } + + /* + * Move the coroutine from iohandler_ctx to qemu_aio_context for + * executing the command handler so that it can make progress if it + * involves an AIO_WAIT_WHILE(). + */ + aio_co_schedule(qemu_get_aio_context(), qmp_dispatcher_co); + qemu_coroutine_yield(); + /* Process request */ if (req_obj->req) { if (trace_event_get_state(TRACE_MONITOR_QMP_CMD_IN_BAND)) {