From mboxrd@z Thu Jan 1 00:00:00 1970 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 lists1p.gnu.org (lists1p.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 8C22BC4450A for ; Thu, 16 Jul 2026 10:20:37 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wkJCR-00040S-Gj; Thu, 16 Jul 2026 06:20:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wkJCO-000403-Ih for qemu-devel@nongnu.org; Thu, 16 Jul 2026 06:20:12 -0400 Received: from [115.124.30.124] (helo=out30-124.freemail.mail.aliyun.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wkJCI-00054j-9p for qemu-devel@nongnu.org; Thu, 16 Jul 2026 06:20:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1784197195; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=Qi8jL2Z+EwBGgRPNYf4vM9alBFo+pHcArfdwBiOMkxY=; b=BgCnz46ZT0uVy3i6daEd7PbVlauqSVba9HWmaRo9PgHlKzeO1vjHsAiN7FrC0vTzSriaJJMKOE/jfaTDr9OWyq5L6hgEXkl/FclNqv4XOxJrs3v8Tr2SkNMULwhpXDe+RXrvwH6cvi4261sAOa03a+jfWd5IcaMyReDnn+HgXJ0= X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R941e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=maildocker-contentspam033037026112; MF=guobin@linux.alibaba.com; NM=1; PH=DS; RN=3; SR=0; TI=SMTPD_---0X7E6Rlx_1784197194; Received: from localhost(mailfrom:guobin@linux.alibaba.com fp:SMTPD_---0X7E6Rlx_1784197194 cluster:ay36) by smtp.aliyun-inc.com; Thu, 16 Jul 2026 18:19:54 +0800 From: Bin Guo To: qemu-devel@nongnu.org Cc: peterx@redhat.com, farosas@suse.de Subject: [PATCH 1/3] migration: fix ineffective overflow assert in postcopy blocktime Date: Thu, 16 Jul 2026 18:19:50 +0800 Message-ID: <20260716101952.65329-2-guobin@linux.alibaba.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260716101952.65329-1-guobin@linux.alibaba.com> References: <20260716101952.65329-1-guobin@linux.alibaba.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Host-Lookup-Failed: Reverse DNS lookup failed for 115.124.30.124 (deferred) Received-SPF: pass client-ip=115.124.30.124; envelope-from=guobin@linux.alibaba.com; helo=out30-124.freemail.mail.aliyun.com X-Spam_score_int: -166 X-Spam_score: -16.7 X-Spam_bar: ---------------- X-Spam_report: (-16.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, ENV_AND_HDR_SPF_MATCH=-0.5, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_PASS=-0.001, T_SPF_HELO_TEMPERROR=0.01, UNPARSEABLE_RELAY=0.001, USER_IN_DEF_DKIM_WL=-7.5, USER_IN_DEF_SPF_WL=-7.5 autolearn=no 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org vcpu_faults_current[] is uint8_t. The overflow assert was checked after the post-increment, so 255 would wrap to 0 and the assert would pass silently. Move the check before the increment and use < 255. Signed-off-by: Bin Guo --- migration/postcopy-ram.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c index f5ef93f193..341cad264a 100644 --- a/migration/postcopy-ram.c +++ b/migration/postcopy-ram.c @@ -1093,7 +1093,11 @@ void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid, /* * Account how many concurrent faults on this vCPU we trapped. See * comments above vcpu_faults_current[] on why it can be more than one. + * + * vcpu_faults_current[] is uint8_t, so assert before incrementing to + * catch overflow before it wraps. */ + assert(dc->vcpu_faults_current[cpu] < 255); if (dc->vcpu_faults_current[cpu]++ == 0) { dc->smp_cpus_down++; /* @@ -1103,9 +1107,6 @@ void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid, */ dc->last_begin = current; } - - /* Making sure it won't overflow - it really should never! */ - assert(dc->vcpu_faults_current[cpu] <= 255); } else { /* * For non-vCPU thread faults, we don't care about tid or cpu index -- 2.50.1 (Apple Git-155)