From patchwork Tue May 2 18:41:32 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13229223 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 E72A5C77B73 for ; Tue, 2 May 2023 18:42:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ptuwk-0000E3-ON; Tue, 02 May 2023 14:41:54 -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 1ptuwc-0000Bw-By for qemu-devel@nongnu.org; Tue, 02 May 2023 14:41:46 -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 1ptuwa-0006VT-Dv for qemu-devel@nongnu.org; Tue, 02 May 2023 14:41:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683052903; 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: content-transfer-encoding:content-transfer-encoding; bh=1dQjO7TXO8l7MQRQ7B2Zn5Aa7CrAGDw85wqFlKjOJT0=; b=eeXiHi3HF5ObMXL/brdtN4ZhRgRbZLe/mTc9aforR6E5oNwtvocelXhFliw/kJAux5CLKX 0O+zOO8BQ/u9/FAyVQXdr2RwRM3qeT2mOLumpw8el74k/CSdCxj2bTSElcuA88KAknruai u4lY/LrOCtZVSAS0CB8OVgTsvl4t+RA= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-204-VO2D25BONK6CA3xgX2NUGQ-1; Tue, 02 May 2023 14:41:40 -0400 X-MC-Unique: VO2D25BONK6CA3xgX2NUGQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E24243850547; Tue, 2 May 2023 18:41:36 +0000 (UTC) Received: from localhost (unknown [10.39.192.230]) by smtp.corp.redhat.com (Postfix) with ESMTP id 492E563F4A; Tue, 2 May 2023 18:41:36 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Fam Zheng , Paolo Bonzini , Stefan Hajnoczi , qemu-block@nongnu.org Subject: [PATCH 0/2] aio-posix: do not nest poll handlers Date: Tue, 2 May 2023 14:41:32 -0400 Message-Id: <20230502184134.534703-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 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: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.171, 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_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: 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 following stack exhaustion was reported in https://bugzilla.redhat.com/show_bug.cgi?id=2186181: ... #51 0x000055884fca7451 aio_poll (qemu-kvm + 0x9d6451) #52 0x000055884fab9cbd bdrv_poll_co (qemu-kvm + 0x7e8cbd) #53 0x000055884fab654b blk_io_plug (qemu-kvm + 0x7e554b) #54 0x000055884f927fef virtio_blk_handle_vq (qemu-kvm + 0x656fef) #55 0x000055884f96d384 virtio_queue_host_notifier_aio_poll_ready (qemu-kvm + 0x69c384) #56 0x000055884fca671b aio_dispatch_handler (qemu-kvm + 0x9d571b) #57 0x000055884fca7451 aio_poll (qemu-kvm + 0x9d6451) #58 0x000055884fab9cbd bdrv_poll_co (qemu-kvm + 0x7e8cbd) #59 0x000055884fab654b blk_io_plug (qemu-kvm + 0x7e554b) #60 0x000055884f927fef virtio_blk_handle_vq (qemu-kvm + 0x656fef) #61 0x000055884f96d384 virtio_queue_host_notifier_aio_poll_ready (qemu-kvm + 0x69c384) #62 0x000055884fca671b aio_dispatch_handler (qemu-kvm + 0x9d571b) #63 0x000055884fca7451 aio_poll (qemu-kvm + 0x9d6451) ... This happens because some block layer APIs in QEMU 8.0 run in coroutines in order to take the graph rdlock. Existing virtqueue handler functions weren't written with this in mind. A simplified example of the problem is: void my_fd_handler(void *opaque) { do_something(); event_notifier_test_and_clear(opaque); do_something_else(); } When do_something() calls aio_poll(), my_fd_handler() will be entered again immediately because the fd is still readable and stack exhaustion will occur. When do_something_else() calls aio_poll(), there is no stack exhaustion since the event notifier has been cleared and the fd is not readable. The actual bug is more involved. The handler in question is a poll handler, not an fd handler, but the principle is the same. I haven't been able to reproduce the bug, but I have included a test case that demonstrates the problem. Stefan Hajnoczi (2): aio-posix: do not nest poll handlers tested: add test for nested aio_poll() in poll handlers tests/unit/test-nested-aio-poll.c | 130 ++++++++++++++++++++++++++++++ util/aio-posix.c | 11 +++ tests/unit/meson.build | 1 + 3 files changed, 142 insertions(+) create mode 100644 tests/unit/test-nested-aio-poll.c