From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SN4PR0501CU005.outbound.protection.outlook.com (mail-southcentralusazon11011000.outbound.protection.outlook.com [40.93.194.0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E6DE4F3EB9 for ; Mon, 28 Sep 2026 17:19:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.194.0 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790615990; cv=fail; b=ZfFzUI4Q5mlmPDJ6zOqepREW9VjxkIl7kpZnsTgytIQq9JT822iRiKpidQjStHv2WEtTDVo4+svqTVLKQmnX6bNMOR5gQSN4KkVlntOVD7ZYgPnPhIAwoYIJkYstJu8Vod0tD4LREPzpXm9cAeGfMGIXic94WmpQX68HVfbnX4o= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790615990; c=relaxed/simple; bh=04LLXglSyn6qM2VtNnUXs6+yCiH+n/m2wI6koUurWug=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=MHlUf9yylKZ0wpnJ/tohr3qIhphkOHo6jxCUVCpsjF7Bu9Dm8RZQ+dqNTLaLB9OdfjBJsNjvGGeD3yUaY+G/SNgE389lmITCada75QmaPrrl3W/NCqCECIz3Kg85/kappzzo835LL99p4JS6mU3SCVAPgPDsorkk8rZQqgLzmyg= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=KnjPPNH6; arc=fail smtp.client-ip=40.93.194.0 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="KnjPPNH6" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=dXrscFWxq2S6m893eqx0RDLKTEIBsPSVmKWRqK6Q+1DEgf0NdkwaW2aDstBNDlSY6F0rLZZyfgg3uY+vO8N1reqctVgBOIm29mDo5jH0/Rx9i78U2JTTgUkcmlGhBkLsTH159/vGgEXXLHLlPLUH6TlKAiWzNMRMkSSIyrpMnZ+HRSFKLZJHlxX70lLKYV1IhtKeKGmmtwx+43EgHxOxOiHNZO2+2XpkZI+dHobTDBGzZ3NGqT84gxQgwpFqqdr5/baf/D6eUkmk+BxD/8fQafTo3T89UXVQkCxdQbZLEPKeZk/Jyy5zfoHYiIYi9KeOhaHG9MhUNtf3yVGgzyrRBg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=GZtkim0TEt2R4BVatTpczKpUCRFTCWcw7PTbfeeplgU=; b=hVQr2z4/ToGByltiJUWVDeQqAnDQBDDJcw30VWBD/3XmYBHao2oaRN5keVVBitZVgVJ0asXwd2Fsx2eosW8Uyw8VMeKcFi3rwXqkrrFfp1wsVjS3oM3EO2CDthi194Zvj1+JzDs10E65bmpwmZVNgM+2DbvTb/XEgsXIdec9dCnrsPPwR5IUPVTpfjpPWitdTan/NoFLU3UZGHylCxSTtFidUcnTvBrsvC9dgDybrUHm89GTiHtnyajrjN2NWybUmTS/vCMnLxcm5VcAGKzGmT0NKY1KQxRucqlqomlcrTRp+VAPNDQBj/BrAlxKzEvSiGsYqihn0sezY4vLeT08Ig== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=GZtkim0TEt2R4BVatTpczKpUCRFTCWcw7PTbfeeplgU=; b=KnjPPNH65nT0g9SIaqG24ABZj0BbmnYMC2S2/diMb8c+7WufzeMy1VfSvlePt9dcxymodjnFWSz+NtJhUZ3MGkyehyTrGGUbm33hNaGXSovPDyLv+wM+sl5hR/H/A1xyM+R3nmAmhgu0sTx1cearlq1XQRluaY+Kynf3hCwilvac86qcCT45qE1bPv1U6MWNWz+6RsoFzkpp8+lBbtG/LmmIe6eST3jfRzYajdXLK5eneC0ytvRhLMPuq4XIxZg/lFty/oSBUOzeX6KFj6lv65ENGmfmqcMKdWUR5IyIFZ0xPz4Py+Q/LH5g3Un9L98dfqUfCV8XILRZl55984Sukg== Authentication-Results: mx.microsoft.com 1; dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) by SJ2PR12MB8739.namprd12.prod.outlook.com (2603:10b6:a03:549::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.451.23; Mon, 28 Sep 2026 17:19:38 +0000 Received: from DM6PR12MB4827.namprd12.prod.outlook.com ([fe80::6261:3040:864b:159c]) by DM6PR12MB4827.namprd12.prod.outlook.com ([fe80::6261:3040:864b:159c%6]) with mapi id 15.21.0451.022; Mon, 28 Sep 2026 17:19:38 +0000 Date: Mon, 28 Sep 2026 19:19:26 +0200 From: Andrea Righi To: Sechang Lim Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Gabriele Monaco , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] sched: set TIF_NEED_RESCHED before calling __trace_set_need_resched() Message-ID: References: <20260630084750.2792851-1-rhkrqnwk98@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260630084750.2792851-1-rhkrqnwk98@gmail.com> X-ClientProxiedBy: MI1P293CA0019.ITAP293.PROD.OUTLOOK.COM (2603:10a6:290:3::16) To DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR12MB4827:EE_|SJ2PR12MB8739:EE_ X-MS-Office365-Filtering-Correlation-Id: 9b8eacbe-54ae-455d-3d63-08df1d84ac5b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|366016|376014|7416014|10067099003|11063799006|56012099006|6133799003|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: hNrQoeCrnsrwM3EHHR+TN0JQo2EmvLZSE2WUn4xG03PFLaM6G917acfhMQ7U/8WqTTUkuiznUiccLdoalDHPm6dfO8W/ZJFtADaAWeVle6ePdC7nOZ7Kyob1G+TyqJcOJsHIxrt34jpeNDwH5ZlWr5cTOPX/6F7G/Vh/oycuiTnP1T/Fp8M2zttFO/I5HdW8cpzAsADM9n991QTCYdstjWu2AKTpZ1qD80C3rRQG1iGYU+57KnAbFmxio+qICw+/G2yPCCIqP87k2nneZLyLTCDH/h6Ut8UaMuAUMXvxVL7+WWqJlK9qdJsSsCxTMJ8TR54z48e1pFHWiBJkqAsCYXYn7SDc/opUHTqucFjONP7Maznd4BomhtzHMS9xPyVs880Z51MosNxRivSrhs4b83FoRSJhAteaax5O8lMxh48ENsRspg9EKubNEZ8qEcpzmJoq6Yf473yXiWt1Nw35Xifv/baeSEqOaMYb6Js/9zx5oD+0SEmjgTJCsKW96GPEPW1FX4pctxhTxmCtKpjpSMB3a80ZGRVjSzemmqDP4T8fnSJePxPBHQB1mjAAJWD3aBiy7qqJ8erf31H6t59vb3mD7EIGlsdLUBhl0tkcMQdMHzT+Y7NABgWavh/v1OfdcyIM1q3auq43Rbbd+OLWvsZrO8xYXurDEz7+ROEmNlE= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR12MB4827.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(23010399003)(366016)(376014)(7416014)(10067099003)(11063799006)(56012099006)(6133799003)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?3QpxCrwRf2t3WEzq1vZNDhQB5o8ipS3MmTvUv4ueSLTe68KfUi6vn341ZRJJ?= =?us-ascii?Q?Ypyp8y76uwCcNhKrJ5giwFmenZhFPgerLFy8D9dLk5ptmW2UeJEuvpxyxuDy?= =?us-ascii?Q?3c78GczoAEviEKFrxne00KwAGRKSYejppmTXHlfQRh2PSgmh1FomaTTHFhXX?= =?us-ascii?Q?p+abrst2TJ9/VMU6OXqoUntge4cBuXnn+8iZ1uZbwguEnTGxotodfZuAitkM?= =?us-ascii?Q?WPb1n6ro6e9TUzp6pEw4yMceytBOI/XufEh7Gsa2dfzcbqfwtUtu5xX8dwjk?= =?us-ascii?Q?+YdXHRDDT1T56pKk7/NduxnYilXQq3y1gGqZFEQBIqmTQQ5X7CgDfSJd1R0g?= =?us-ascii?Q?JpnrnGjDQxILt0M9ouD/L460zWSQRXd49vGDDxx6Ixp5LX8VVMBWZoZkzctu?= =?us-ascii?Q?qNzbMnnki6aczWpezWzjYtgVXEpNmLhstcYzWZM5tnBC4XuO4XG9F+9U+m03?= =?us-ascii?Q?+h6e7Fcmi8HMjoreiqRgnINDONGZJzr6BSyrwkljao3eX/JgHhWFfL8Y7m/p?= =?us-ascii?Q?o+8U+cWMbn8pci3dEIEsRso00QgOUrVXokqQBWHDs6MDy6Mvqa/GXLBtQgPw?= =?us-ascii?Q?2ThcKRxGTO8mjwLoelEVBKrZ/+sKyHdaybz1FAdPMcRguCi/PCuVKu5KVGr/?= =?us-ascii?Q?ftL5OF3oAUvg5DsBJY0Y1J1gDKz4ZZ1t4UNWkRwK+jyamrAnxMYh2V+hf6xg?= =?us-ascii?Q?7Tuw2zBbRRR8G21H4P7TlngiwG5J8j2IzOp2YjLEk/Jzy5HemAgeWMA2JYm/?= =?us-ascii?Q?sejJ2MiaoCXywzLo72YPOAY/mxSUhIFW6rtWaKCkobg+AWBQbzwH0FcyUkjx?= =?us-ascii?Q?LDZIOPSyawRT15kHBKR6BnmbLAHdujqjRZIRJz80sSoMSROy18bMYVjZxIrL?= =?us-ascii?Q?cp/aDb9cQjnkgdl7DRObl3hXfJyuS5UrvvIOoBVSvNiY48Ph7RmQPJcYju6B?= =?us-ascii?Q?W3hxpUCxTaojjXuzWpSW9nEJAXR57Wpj/zrqfCB2fdAS1vV+ehzA3uKCPNZf?= =?us-ascii?Q?UloGS3/i7Iqdkp1Usf8nzVpCv6hExsLJJO3wO4fQGlYbkmaFA5IZDaeFm0hW?= =?us-ascii?Q?uDd6eeePFNALWt74QZuJku5vbQiP/mhVKiR0hTjnTW+OcmDfZJXOJzCLauBq?= =?us-ascii?Q?pIa1kXViVKbjx26vpr0LLdIASl3lY5OJBJFUgJ8NXbZcyd1qRfsM8jxHbv8s?= =?us-ascii?Q?KNHHb6FTJ7GXatNu5vELVaD6PGrFOdhTGx/5M1V7aJ0T/JT7YsH4jhCoDJHk?= =?us-ascii?Q?/kjbQgsRFgg9VEZqrKAaUkEVgKXumjFW0RlSc0bFEtlqb692J3HsX2PNbesR?= =?us-ascii?Q?mEk0NUZMTIA2nEiScLh/Y/U8qNOddg+9MJn7HnDilqUeNrcFi+DyX6VF4QAa?= =?us-ascii?Q?Wss1ze516+O6rvRqzApdH3YQYfB2/KdMm44qeKoG6CZU3vJL6owfwaZY8yf0?= =?us-ascii?Q?nN/f1V1yB1X28diqUT1r+A8gBz1KmzKtXmR+6ltRXdp3l0ylbWjDmhOq5cPX?= =?us-ascii?Q?iXEB/jYS/jGXMuPHrizQoI9L2MP1EWFHN2+9rHCB80TOVComJSRfqSXRk30y?= =?us-ascii?Q?f9Xd/fGGIiQPRy7TWJPAY/ofGB8zF7XTxB66juvl9Jx/P0edt0QTnKN7Ozp6?= =?us-ascii?Q?Yrm0JYozonGbHRbnz39c5UlhzSXUzjp/FXph9Y3yDQYrNFBytPJ3QcaGEAec?= =?us-ascii?Q?1rMSciYI2VIpURO7Gd/W6emxsUJalx97j9jQdkGv7Jn2var2QB20ImD6g9Tk?= =?us-ascii?Q?GF9uwRhLGA=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9b8eacbe-54ae-455d-3d63-08df1d84ac5b X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB4827.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Sep 2026 17:19:37.9780 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: RZYlUyozMDIuDB6fh8amIF7IZV+zCjXawowU3YTC0d3kr8OyWMN9e+dpkS+N+vggQ0qOSjUQLzVC4k8/cdY5lQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8739 Hi Sechang, On Tue, Jun 30, 2026 at 08:47:37AM +0000, Sechang Lim wrote: > set_tsk_need_resched() tests TIF_NEED_RESCHED, calls > __trace_set_need_resched() if the flag is clear, then sets it via > set_tsk_thread_flag(). A BPF raw_tp program attached to > sched_set_need_resched executes synchronously inside __bpf_trace_run(). > On return, __bpf_trace_run() drops the RCU lock with > rcu_read_unlock_migrate(), which on the preempt-or-BH-disabled path > calls set_need_resched_current() -> set_tsk_need_resched() again. > > set_tsk_thread_flag() follows the tracepoint call, so every re-entrant > frame sees TIF_NEED_RESCHED clear and calls __trace_set_need_resched() > again: > > BUG: TASK stack guard page was hit at ffffc9001224ff98 > Oops: stack guard page: 0000 [#1] SMP KASAN PTI > RIP: 0010:__bpf_trace_sched_set_need_resched_tp+0x1c/0x190 > Call Trace: > trace_sched_set_need_resched_tp+0x110/0x130 > set_tsk_need_resched include/linux/sched.h:2076 > set_need_resched_current include/linux/sched.h:2094 > rcu_read_unlock_special+0x43a/0x440 > __rcu_read_unlock+0x9e/0x120 > rcu_read_unlock_migrate+0xa9/0x240 > __bpf_trace_run+0x131/0x180 > bpf_trace_run3+0x333/0x430 > __bpf_trace_sched_set_need_resched_tp+0x13a/0x190 > trace_sched_set_need_resched_tp+0x110/0x130 > set_tsk_need_resched include/linux/sched.h:2076 > ... > > __resched_curr() has the same ordering, firing the tracepoint before > setting the flag via set_ti_thread_flag() or set_nr_and_not_polling(). > Fix it for consistency. > > Replace the separate test_tsk_thread_flag() + set_tsk_thread_flag() pair > in set_tsk_need_resched() with test_and_set_tsk_thread_flag(). In > __resched_curr(), move the tracepoint call after the flag is set in > each path. This leaves the race Prateek described in the v2 discussion: a remote CPU sets TIF_NEED_RESCHED under rq->lock, but the target CPU can emit sched_entry_tp() before acquiring that lock, ahead of the need-resched tracepoint. I reproduced it with this applied to tip/master. With the RV nrp monitor enabled, 300 runs of "perf bench sched messaging -g 20 -l 100" produced: rv: monitor nrp does not allow event schedule_entry_preempt on state any_thread_running Applying the following on top fixed the ordering, the same 300-run test then completed without an RV violation. If it makes sense, could you fold this change into v4? Thanks, -Andrea diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 639b5df7cf130..91a15a4234280 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7143,9 +7143,6 @@ static void __sched notrace __schedule(int sched_mode) struct rq *rq; int cpu; - /* Trace preemptions consistently with task switches */ - trace_sched_entry_tp(sched_mode == SM_PREEMPT); - cpu = smp_processor_id(); rq = cpu_rq(cpu); prev = rq->curr; @@ -7178,6 +7175,9 @@ static void __sched notrace __schedule(int sched_mode) rq_lock(rq, &rf); smp_mb__after_spinlock(); + /* Trace preemptions consistently with task switches */ + trace_sched_entry_tp(sched_mode == SM_PREEMPT); + hrtick_schedule_enter(rq); /* Promote REQ to ACT */ > > Fixes: adcc3bfa8806 ("sched: Adapt sched tracepoints for RV task model") > Signed-off-by: Sechang Lim > --- > v3: > - reorder need_ipi variable. (K Prateek Nayak) > > v2: > - https://lore.kernel.org/all/20260627081657.499781-1-rhkrqnwk98@gmail.com/ > > v1: > - https://lore.kernel.org/all/20260625065656.392182-1-rhkrqnwk98@gmail.com/ > > include/linux/sched.h | 5 ++--- > kernel/sched/core.c | 7 +++++-- > 2 files changed, 7 insertions(+), 5 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index ee06cba5c6f5..c9efd08dae92 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -2071,10 +2071,9 @@ static inline int test_tsk_thread_flag(struct task_struct *tsk, int flag) > > static inline void set_tsk_need_resched(struct task_struct *tsk) > { > - if (tracepoint_enabled(sched_set_need_resched_tp) && > - !test_tsk_thread_flag(tsk, TIF_NEED_RESCHED)) > + if (!test_and_set_tsk_thread_flag(tsk, TIF_NEED_RESCHED) && > + tracepoint_enabled(sched_set_need_resched_tp)) > __trace_set_need_resched(tsk, TIF_NEED_RESCHED); > - set_tsk_thread_flag(tsk,TIF_NEED_RESCHED); > } > > static inline void clear_tsk_need_resched(struct task_struct *tsk) > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b8871449d3c6..19de28f0d85a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1171,6 +1171,7 @@ static void __resched_curr(struct rq *rq, int tif) > { > struct task_struct *curr = rq->curr; > struct thread_info *cti = task_thread_info(curr); > + bool need_ipi; > int cpu; > > lockdep_assert_rq_held(rq); > @@ -1187,15 +1188,17 @@ static void __resched_curr(struct rq *rq, int tif) > > cpu = cpu_of(rq); > > - trace_sched_set_need_resched_tp(curr, cpu, tif); > if (cpu == smp_processor_id()) { > set_ti_thread_flag(cti, tif); > if (tif == TIF_NEED_RESCHED) > set_preempt_need_resched(); > + trace_sched_set_need_resched_tp(curr, cpu, tif); > return; > } > > - if (set_nr_and_not_polling(cti, tif)) { > + need_ipi = set_nr_and_not_polling(cti, tif); > + trace_sched_set_need_resched_tp(curr, cpu, tif); > + if (need_ipi) { > if (tif == TIF_NEED_RESCHED) > smp_send_reschedule(cpu); > } else { > -- > 2.43.0 >