From nobody Wed Feb 11 13:27:53 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9CC8C7EE22 for ; Mon, 8 May 2023 22:32:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233958AbjEHWb7 (ORCPT ); Mon, 8 May 2023 18:31:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229726AbjEHWb5 (ORCPT ); Mon, 8 May 2023 18:31:57 -0400 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E9445BB4 for ; Mon, 8 May 2023 15:31:56 -0700 (PDT) Received: from pps.filterd (m0246632.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 348JOqYU002193; Mon, 8 May 2023 22:31:45 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding; s=corp-2023-03-30; bh=XrK/JXU+hKQB6UYMoHY7BZ0MAhaISZxQ8B5BJOL3qro=; b=ZqeLt0eR/Ob78wA1D9IsHB67IRe2CyVPaI18DIVSTO/aKx4ts4HIL/AyXewlMBrZ+Ecd WX0uJKr4F/WZWw75kk0djbWtqiCTbjyYQJqKzU5wVnqqnxBqoegprrStTjBfUzLFOBt7 FIbUjQUMTD9HsEuslsJopkzN6+SHItVF1WyvyzKDHL4A5rl7Y3xyYMU8pSNxpZ1rJCXg BQP3dNlwTE5c9zvBAvk/p36Syng45Mtmo+xsQv8q5CN7//J/MIBBl0hI0mVP4Mp6ImpP VZQ9Pa8v8TwyIeLhRWxUHZpLri4w7a1qyq5ib+/9LGXY0gy5o4sZpPuh52X5FtUPxrhl Gw== Received: from iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta01.appoci.oracle.com [130.35.100.223]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3qf7770ah4-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 08 May 2023 22:31:45 +0000 Received: from pps.filterd (iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (8.17.1.19/8.17.1.19) with ESMTP id 348LZueZ015246; Mon, 8 May 2023 22:31:44 GMT Received: from localhost.localdomain (dhcp-10-191-130-46.vpn.oracle.com [10.191.130.46]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 3qf77f5pca-2; Mon, 08 May 2023 22:31:44 +0000 From: Imran Khan To: peterz@infradead.org, paulmck@kernel.org, jgross@suse.com, vschneid@redhat.com, yury.norov@gmail.com, tglx@linutronix.de Cc: linux-kernel@vger.kernel.org Subject: [RESEND PATCH 1/2] smp: Reduce logging due to dump_stack of CSD waiters. Date: Tue, 9 May 2023 08:31:23 +1000 Message-Id: <20230508223124.1438167-2-imran.f.khan@oracle.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230508223124.1438167-1-imran.f.khan@oracle.com> References: <20230508223124.1438167-1-imran.f.khan@oracle.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-05-08_16,2023-05-05_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 malwarescore=0 adultscore=0 spamscore=0 mlxscore=0 phishscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305080149 X-Proofpoint-GUID: _fkGR7T4gLbh6PYqry66MmP2USW6qBbc X-Proofpoint-ORIG-GUID: _fkGR7T4gLbh6PYqry66MmP2USW6qBbc Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" If a waiter is waiting for CSD lock, its call stack will not change between first and subsequent hang detection for the same CSD lock. So dump_stack for the waiter only for first time detection. This avoids excessive logging on large scale systems(with hundreds of CPUs) where repetitive dump_stack from hundreds of CPUs can flood the console. Signed-off-by: Imran Khan Reviewed-by: Paul E. McKenney --- kernel/smp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/smp.c b/kernel/smp.c index ab3e5dad6cfe9..b7ccba677a0a0 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -248,7 +248,8 @@ static bool csd_lock_wait_toolong(struct __call_single_= data *csd, u64 ts0, u64 * arch_send_call_function_single_ipi(cpu); } } - dump_stack(); + if (firsttime) + dump_stack(); *ts1 =3D ts2; =20 return false; --=20 2.34.1 From nobody Wed Feb 11 13:27:53 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A3AD8C77B75 for ; Mon, 8 May 2023 22:32:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234015AbjEHWcC (ORCPT ); Mon, 8 May 2023 18:32:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233976AbjEHWb7 (ORCPT ); Mon, 8 May 2023 18:31:59 -0400 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F07A665AA for ; Mon, 8 May 2023 15:31:58 -0700 (PDT) Received: from pps.filterd (m0246632.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 348JOsrS002212; Mon, 8 May 2023 22:31:48 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding; s=corp-2023-03-30; bh=B9yD/+CYrKVcypcEgjmGEaQX//z09PC+3sHaWn9qNXY=; b=fip0cDRmD8TGviS8pvRKyVtChRoKOPG4Uqplmf2abB2QcojmY1eCz5DLB2pLzNRgncMH uTfDfdYcK21C6QvR3vjRC7L44pFQ1M1vmWusmcg0fUskZe80tf9XSie5VXF9M3MKqYRh KzOBmZQlVz8LcGF1iG/g4LDjmrwF2HsHPB6DIcxxnRWczbxVrpnwgMqdZzV8exidM/Ma k2J+xvWY0tAeFuOEI4BfcSyXV7em+Msee1ed/MT2Luf5LS3PUCeBWkwFphD8wSCdreAd LibmmQPyRerz/Eo/b71/wSANSs1vBLO8IXMLhyE8oT2Zw2P7jB4DOenw7plQ+EWopzIb Gg== Received: from iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta01.appoci.oracle.com [130.35.100.223]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3qf7770ah6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 08 May 2023 22:31:48 +0000 Received: from pps.filterd (iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (8.17.1.19/8.17.1.19) with ESMTP id 348LZuea015246; Mon, 8 May 2023 22:31:48 GMT Received: from localhost.localdomain (dhcp-10-191-130-46.vpn.oracle.com [10.191.130.46]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 3qf77f5pca-3; Mon, 08 May 2023 22:31:47 +0000 From: Imran Khan To: peterz@infradead.org, paulmck@kernel.org, jgross@suse.com, vschneid@redhat.com, yury.norov@gmail.com, tglx@linutronix.de Cc: linux-kernel@vger.kernel.org Subject: [RESEND PATCH 2/2] smp: Reduce NMI traffic from CSD waiters to CSD destination. Date: Tue, 9 May 2023 08:31:24 +1000 Message-Id: <20230508223124.1438167-3-imran.f.khan@oracle.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230508223124.1438167-1-imran.f.khan@oracle.com> References: <20230508223124.1438167-1-imran.f.khan@oracle.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-05-08_16,2023-05-05_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 malwarescore=0 adultscore=0 spamscore=0 mlxscore=0 phishscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305080149 X-Proofpoint-GUID: rDEMgUGpwh1Lrqbkr3GQOK8wEb2tQVkb X-Proofpoint-ORIG-GUID: rDEMgUGpwh1Lrqbkr3GQOK8wEb2tQVkb Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" On systems with hundreds of CPUs, if few hundred or most of the CPUs detect a CSD hang, then all of these waiters endup sending an NMI to destination CPU to dump its backtrace. Depending on the number of such NMIs, destination CPU can spent a significant amount of time handling these NMIs and thus making it more difficult for this CPU to address those pending CSDs timely. In worst case it can happen that by the time destination CPU is done handling all of the above mentioned backtrace NMIs, csd wait time may have elapsed and all of the waiters start sending backtrace NMI again and this behaviour continues in loop. To avoid the above mentioned scenario, issue backtrace NMI only from first waiter. The other waiters to same CSD destination can make use of backtrace obtained via fist waiter's NMI. Signed-off-by: Imran Khan Reviewed-by: Paul E. McKenney --- kernel/smp.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/smp.c b/kernel/smp.c index b7ccba677a0a0..a1cd21ea8b308 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -43,6 +43,8 @@ static DEFINE_PER_CPU_ALIGNED(struct call_function_data, = cfd_data); =20 static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue); =20 +static DEFINE_PER_CPU(atomic_t, trigger_backtrace) =3D ATOMIC_INIT(1); + static void __flush_smp_call_function_queue(bool warn_cpu_offline); =20 int smpcfd_prepare_cpu(unsigned int cpu) @@ -242,7 +244,8 @@ static bool csd_lock_wait_toolong(struct __call_single_= data *csd, u64 ts0, u64 * *bug_id, !cpu_cur_csd ? "unresponsive" : "handling this request"); } if (cpu >=3D 0) { - dump_cpu_task(cpu); + if (atomic_cmpxchg_acquire(&per_cpu(trigger_backtrace, cpu), 1, 0)) + dump_cpu_task(cpu); if (!cpu_cur_csd) { pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\= n", *bug_id, raw_smp_processor_id(), cpu); arch_send_call_function_single_ipi(cpu); @@ -423,9 +426,14 @@ static void __flush_smp_call_function_queue(bool warn_= cpu_offline) struct llist_node *entry, *prev; struct llist_head *head; static bool warned; + atomic_t *tbt; =20 lockdep_assert_irqs_disabled(); =20 + /* Allow waiters to send backtrace NMI from here onwards */ + tbt =3D this_cpu_ptr(&trigger_backtrace); + atomic_set_release(tbt, 1); + head =3D this_cpu_ptr(&call_single_queue); entry =3D llist_del_all(head); entry =3D llist_reverse_order(entry); --=20 2.34.1