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 CE694C43458 for ; Mon, 6 Jul 2026 11:04:30 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wgh77-0006FH-KW; Mon, 06 Jul 2026 07:03:49 -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 1wgh73-0006Eg-Bv; Mon, 06 Jul 2026 07:03:45 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wgh71-0001Mz-BF; Mon, 06 Jul 2026 07:03:44 -0400 Received: from pps.filterd (m0353725.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 6669ILml3151332; Mon, 6 Jul 2026 11:03:40 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:date:from:in-reply-to:message-id :mime-version:references:subject:to; s=pp1; bh=5o5XWdgPq9rHSafYv Pw5xydqCTMb2BI5zpTiZWNKpss=; b=cc0aYpuegrCHexBRlwXausTuNnutnDtJ7 peiu4tMR6JgdBoYX5xd5O02hkDFKCuU36t6s9/rfDHBI5yGwnVD0l63D8RQdNFZn ze4dAtdPtjUY7KRUFTBqxbwwrmzUlAa9hMRnhbbrkbW1o+skAUs+4obiBfC1QMG6 pRsDKR0BE3EVD8/H4V0KGlH01324me1F4xp6ei3atGAdxbuSAzLVFvpZ8Hgp5ofz 6LSQa121xALZ+y0O3hYhBVgNF4LQJgGap10fdxqUfniFTJ5V9Qj6s2N/AxX2wQJN vzzMeN+fvJuDKhftyyQ4JOAERZZlmywenaCvUPjNCs09P0w1z8UGA== Received: from ppma13.dal12v.mail.ibm.com (dd.9e.1632.ip4.static.sl-reverse.com [50.22.158.221]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4f6rkdhpa1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 06 Jul 2026 11:03:39 +0000 (GMT) Received: from pps.filterd (ppma13.dal12v.mail.ibm.com [127.0.0.1]) by ppma13.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 666AncbU002940; Mon, 6 Jul 2026 11:03:39 GMT Received: from smtprelay05.fra02v.mail.ibm.com ([9.218.2.225]) by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4f7eqfw1jj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 06 Jul 2026 11:03:38 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (smtpav07.fra02v.mail.ibm.com [10.20.54.106]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 666B3YsV50397498 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 6 Jul 2026 11:03:34 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8D0EB2004F; Mon, 6 Jul 2026 11:03:34 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2484420040; Mon, 6 Jul 2026 11:03:34 +0000 (GMT) Received: from heavy.ibm.com (unknown [9.111.23.52]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 6 Jul 2026 11:03:34 +0000 (GMT) From: Ilya Leoshkevich To: Richard Henderson , Paolo Bonzini Cc: qemu-devel@nongnu.org, Ilya Leoshkevich , Alex Crichton , Ulrich Weigand , qemu-stable@nongnu.org Subject: [PATCH 1/1] accel/tcg: Retry page_check_range() on itree.start inconsistency Date: Mon, 6 Jul 2026 12:57:25 +0200 Message-ID: <20260706110330.4150026-2-iii@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260706110330.4150026-1-iii@linux.ibm.com> References: <20260706110330.4150026-1-iii@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=M7J97Sws c=1 sm=1 tr=0 ts=6a4b8b8b cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=NEAV23lmAAAA:8 a=vjliLWF1AAAA:8 a=VnNF1IyMAAAA:8 a=69wJf7TsAAAA:8 a=EA-HjLQVFIEyDo_wN94A:9 a=3erKlr7R_9HjozMBkBTY:22 a=Fg1AiH1G6rFz08G2ETeA:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA2MDEwOSBTYWx0ZWRfX6U1bF4nvmn6Y diTthcFmJUILUuCXVRN/xPGx57xZ5Ey7p8ezFCvtJKwrT3l6y4ORiCo0RFazSztegiQ4hPvNbIZ emjxORTsrENxzyWtDdEda8TRBI4UfbLBwuirE+z9gbcNbzndaSiH0HSiJQhJoD8xnL24EJ2xdtQ PrsRPhC21Yz95uuPXhuFINDdfsYrYjT9zwMv8BR8L+sEwNtYyBHZFWY8xnedegKypqvQ9AVJCAn LMk3izNsJB56z4X6oPZ9BQj8gnDupn2+0i7XA+86kmUdSoUUPYU0ENqIgrygknJZLvcFU31ITfP +ZIgNZUthA0rjij1NvMY9Bkq3XpoYXQgtjxxmIAKkElhCY/o5tNUv3y7mkd49tvkLlh3Sujix+d El3ZJGKneooyCcz59NuxmsAYCKOT/Xk7effR5WW46eG3dBMwD3nT7vw8XEgHm0HmjnHr8E+XhVX DfjNf2L3dYZwNar/p7w== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA2MDEwOSBTYWx0ZWRfX0iLKMA/JaXgk 2PpsRlxVOyt1tCEh+CZHihLSsaeTFwhYQrtPMFaEwInTmlDyxtO/0rFGsdinsYrmStVONnvuEVL EU44rrV72NiH47jtWiZyIMBx++/HeD4= X-Proofpoint-GUID: S9Jx6w5OtwCy8RCS28Ac_A8aLPjRprTD X-Proofpoint-ORIG-GUID: S9Jx6w5OtwCy8RCS28Ac_A8aLPjRprTD X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-06_01,2026-07-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1011 adultscore=0 priorityscore=1501 bulkscore=0 spamscore=0 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607060109 Received-SPF: pass client-ip=148.163.158.5; envelope-from=iii@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org page_check_range() may race with pageflags_set_clear() as follows: T1 T2 ------------------------------------- -------------------------------- p = pageflags_find(start, last); interval_tree_remove(&p->itree, ...); p->itree.start = last + 1; if (start < p->itree.start) { ret = false; interval_tree_insert(&p->itree, ...); leading to errors like fail indirect write 0x72f0a659aff0 (Bad address) in vma-pthread test. I am able to reliably reproduce this on a machine with 32 SMT threads as follows in about 25 seconds: jobs=32; \ seq "$jobs" | \ time -p parallel \ --jobs="$jobs" \ --halt=now,done=1 \ --ungroup \ ' _={}; while ./qemu-s390x tests/tcg/s390x-linux-user/vma-pthread; do printf .; done ' Also wasmtime project reported a similar failure pattern in their CI [1] with a similar reproducer [2]. Fix by retrying under a lock. This makes the failure rate go down to roughly once in 50 seconds. [1] https://github.com/bytecodealliance/wasmtime/issues/10000 [2] https://gist.github.com/alexcrichton/f14f23a892ffb9df2522754572d51b1c Reported-by: Alex Crichton Reported-by: Ulrich Weigand Fixes: 67ff2186b0a4 ("accel/tcg: Use interval tree for user-only page tracking") Cc: qemu-stable@nongnu.org Signed-off-by: Ilya Leoshkevich --- accel/tcg/user-exec.c | 31 +++++++++++++++---------------- 1 file changed, 15 insertions(+), 16 deletions(-) diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c index 7704e4017dd..b70955697fe 100644 --- a/accel/tcg/user-exec.c +++ b/accel/tcg/user-exec.c @@ -510,24 +510,23 @@ bool page_check_range(vaddr start, vaddr len, int flags) PageFlagsNode *p = pageflags_find(start, last); int missing; - if (!p) { - if (!locked) { - /* - * Lockless lookups have false negatives. - * Retry with the lock held. - */ - mmap_lock(); - locked = -1; - p = pageflags_find(start, last); - } - if (!p) { - ret = false; /* entire region invalid */ + /* + * Lockless lookups race with pageflags_set_clear() and may have false + * negatives: + * - The node pageflags_find() was looking for could have been + * temporarily removed and not added back yet. + * - pageflags_find() could have found a node which was subsequently + * removed and whose itree.start has been adjusted. + */ + if (!p || start < p->itree.start) { + if (locked) { + ret = false; break; } - } - if (start < p->itree.start) { - ret = false; /* initial bytes invalid */ - break; + /* Retry with the lock held. */ + mmap_lock(); + locked = -1; + continue; } missing = flags & ~p->flags; -- 2.54.0