From patchwork Tue Mar 3 18:47:51 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dongli Zhang X-Patchwork-Id: 11418689 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 4358F1580 for ; Tue, 3 Mar 2020 18:58:18 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1F4FB206D7 for ; Tue, 3 Mar 2020 18:58:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="mrXy5wOe" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F4FB206D7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1j9CjB-0007pg-0D; Tue, 03 Mar 2020 18:57:13 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1j9Cj9-0007pW-3Y for xen-devel@lists.xenproject.org; Tue, 03 Mar 2020 18:57:11 +0000 X-Inumbo-ID: c91945f4-5d80-11ea-94a0-bc764e2007e4 Received: from userp2120.oracle.com (unknown [156.151.31.85]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id c91945f4-5d80-11ea-94a0-bc764e2007e4; Tue, 03 Mar 2020 18:57:10 +0000 (UTC) Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 023Ir0Xi187016; Tue, 3 Mar 2020 18:57:08 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id; s=corp-2020-01-29; bh=To/HLjUYEZTWO743zz0YfxZ/TOEA4AfwhsEsN360nNs=; b=mrXy5wOeWLiDAiGG5U2dNrZyyOYOJeG3ll/DDA+MOGlF2y7Wr6pefmG5MQryMFraVv8K BAU9t1fHnAPWLhOGM3lnFcc7gK1WoMpqtyHH1NgZzqJebzWRDvnWkQg8FlSLUjiAfBCG w48QTNCoKaX+WeY3PEY+Ob0CLVgYqqriMCT1FofLkBC6L3nwUdwe2fltWoszRyPmLk7b KepjXl4AqXVHCwfoyrbValQfl3ircjla3GWJhr8OXcdTqcBDtF/W4Q7+7F4XDY7Hj8F3 ZIWUX2owcd/AWnCoEknoDz5rEPcK+vjl6LFvEXiYfgN7HYtmEBlrlkwkv1EC1hUpcqIY 8Q== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2120.oracle.com with ESMTP id 2yghn354b1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 03 Mar 2020 18:57:08 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 023IqdlF108404; Tue, 3 Mar 2020 18:57:08 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userp3030.oracle.com with ESMTP id 2yg1emfmd7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 03 Mar 2020 18:57:08 +0000 Received: from abhmp0010.oracle.com (abhmp0010.oracle.com [141.146.116.16]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 023Iv6HI007887; Tue, 3 Mar 2020 18:57:06 GMT Received: from localhost.localdomain (/10.211.9.80) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 03 Mar 2020 10:57:06 -0800 From: Dongli Zhang To: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Date: Tue, 3 Mar 2020 10:47:51 -0800 Message-Id: <20200303184752.20821-1-dongli.zhang@oracle.com> X-Mailer: git-send-email 2.17.1 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9549 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 spamscore=0 mlxlogscore=999 malwarescore=0 bulkscore=0 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2003030124 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9549 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 phishscore=0 spamscore=0 impostorscore=0 mlxscore=0 adultscore=0 mlxlogscore=999 lowpriorityscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2003030124 Subject: [Xen-devel] [PATCH v2 1/2] xenbus: req->body should be updated before req->state X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: jgross@suse.com, joe.jin@oracle.com, boris.ostrovsky@oracle.com, sstabellini@kernel.org, julien@xen.org MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" The req->body should be updated before req->state is updated and the order should be guaranteed by a barrier. Otherwise, read_reply() might return req->body = NULL. Below is sample callstack when the issue is reproduced on purpose by reordering the updates of req->body and req->state and adding delay in code between updates of req->state and req->body. [ 22.356105] general protection fault: 0000 [#1] SMP PTI [ 22.361185] CPU: 2 PID: 52 Comm: xenwatch Not tainted 5.5.0xen+ #6 [ 22.366727] Hardware name: Xen HVM domU, BIOS ... [ 22.372245] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60 ... ... [ 22.392163] RSP: 0018:ffffb2d64023fdf0 EFLAGS: 00010246 [ 22.395933] RAX: 0000000000000000 RBX: 75746e7562755f6d RCX: 0000000000000000 [ 22.400871] RDX: 0000000000000000 RSI: ffffb2d64023fdfc RDI: 75746e7562755f6d [ 22.405874] RBP: 0000000000000000 R08: 00000000000001e8 R09: 0000000000cdcdcd [ 22.410945] R10: ffffb2d6402ffe00 R11: ffff9d95395eaeb0 R12: ffff9d9535935000 [ 22.417613] R13: ffff9d9526d4a000 R14: ffff9d9526f4f340 R15: ffff9d9537654000 [ 22.423726] FS: 0000000000000000(0000) GS:ffff9d953bc80000(0000) knlGS:0000000000000000 [ 22.429898] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 22.434342] CR2: 000000c4206a9000 CR3: 00000001ea3fc002 CR4: 00000000001606e0 [ 22.439645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 22.444941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 22.450342] Call Trace: [ 22.452509] simple_strtoull+0x27/0x70 [ 22.455572] xenbus_transaction_start+0x31/0x50 [ 22.459104] netback_changed+0x76c/0xcc1 [xen_netfront] [ 22.463279] ? find_watch+0x40/0x40 [ 22.466156] xenwatch_thread+0xb4/0x150 [ 22.469309] ? wait_woken+0x80/0x80 [ 22.472198] kthread+0x10e/0x130 [ 22.474925] ? kthread_park+0x80/0x80 [ 22.477946] ret_from_fork+0x35/0x40 [ 22.480968] Modules linked in: xen_kbdfront xen_fbfront(+) xen_netfront xen_blkfront [ 22.486783] ---[ end trace a9222030a747c3f7 ]--- [ 22.490424] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60 The barrier() in test_reply() is changed to virt_rmb(). The "while" is changed to "do while" so that test_reply() is used as a read memory barrier. Signed-off-by: Dongli Zhang --- Changed since v1: - change "barrier()" to "virt_rmb()" in test_reply() drivers/xen/xenbus/xenbus_comms.c | 2 ++ drivers/xen/xenbus/xenbus_xs.c | 11 +++++++---- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c index d239fc3c5e3d..852ed161fc2a 100644 --- a/drivers/xen/xenbus/xenbus_comms.c +++ b/drivers/xen/xenbus/xenbus_comms.c @@ -313,6 +313,8 @@ static int process_msg(void) req->msg.type = state.msg.type; req->msg.len = state.msg.len; req->body = state.body; + /* write body, then update state */ + virt_wmb(); req->state = xb_req_state_got_reply; req->cb(req); } else diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c index ddc18da61834..1e14c2118861 100644 --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -194,15 +194,18 @@ static bool test_reply(struct xb_req_data *req) if (req->state == xb_req_state_got_reply || !xenbus_ok()) return true; - /* Make sure to reread req->state each time. */ - barrier(); + /* + * read req->state before other fields of struct xb_req_data + * in the caller of test_reply(), e.g., read_reply() + */ + virt_rmb(); return false; } static void *read_reply(struct xb_req_data *req) { - while (req->state != xb_req_state_got_reply) { + do { wait_event(req->wq, test_reply(req)); if (!xenbus_ok()) @@ -216,7 +219,7 @@ static void *read_reply(struct xb_req_data *req) if (req->err) return ERR_PTR(req->err); - } + } while (req->state != xb_req_state_got_reply); return req->body; }