From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) (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 2778821D3E8 for ; Wed, 12 Nov 2025 18:08:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=67.231.145.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762970917; cv=none; b=JGvZo43Sg/pwv94vzC1SWYKRJXN8gKlNB/mIlsZ4BZ64Zw6KGg8UkyY7aekToss+o/BEvWPlV1IB8L6Jl8dt3VRg2xSA9HJvUR+K7FcSCSpnuoFLMRTWGDjmSEDAO6whdNNQYcEvORIoxNFF8HfRhlvN5x91uc78JkGWWUdRDXg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762970917; c=relaxed/simple; bh=SVjdf5Aj0rdJj6A5awPo5qb+JCAch7lvbTPIcP4rwcc=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=Pfujtwn9iGFOcbfIAkPXHp4IvXLYGyyZoGnfWyXNUcjZvIcDSA3lEVg84He8z+DN2zMUvUJyFu9sj5L+ZbmFdhBZPJEL61BNujH8ThINWH75ngZsNC6D1gSGv1FoTkZafGGa+16F6PiBj06vpSFGZqBycHFcjGGTiglfO20/3AU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=meta.com; spf=pass smtp.mailfrom=meta.com; dkim=pass (2048-bit key) header.d=meta.com header.i=@meta.com header.b=QDQf8ylS; arc=none smtp.client-ip=67.231.145.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=meta.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=meta.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=meta.com header.i=@meta.com header.b="QDQf8ylS" Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 5ACGQQu11246012 for ; Wed, 12 Nov 2025 10:08:35 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=meta.com; h=cc :content-transfer-encoding:content-type:date:from:message-id :mime-version:subject:to; s=s2048-2025-q2; bh=Tw24IjkIpxorSSaLtl toXikyFgjIwYXd2FO9mDBuUdE=; b=QDQf8ylSJGe2UJKKhYhy2u94pxcno8IkaU hJ6UljUVfqVyb/kIGXc+ZrDnY69Wn8THGAx7zm9mXub9PUxj7Dbo2PM+ZJC4joj8 LVrKqYAE/kHJTZJ/8m665/ht/HOP18KD8dp5NQup857qTMCn+ow4OlRtuIv3IU3R 6lCFZThsDQWugPaNIzqWr52RH/P+aBWrZ0x6J8v/n4ptWOUxr/kq3sieS5niI7Q4 E0QX/9nRX6McyoHJf7EKeP2cq2RcIqSMa92/sxJfs64zmNkirOAtzMAjuGCw3KPS dMT4bxYkPjl8tanvH7dDKyZkhR8AgP7HcyfdT9LmYAWv9B6udZgQ== Received: from maileast.thefacebook.com ([163.114.135.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 4acwrv0xwh-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 12 Nov 2025 10:08:35 -0800 (PST) Received: from twshared125961.16.frc2.facebook.com (2620:10d:c0a8:fe::f072) by mail.thefacebook.com (2620:10d:c0a9:6f::237c) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.20; Wed, 12 Nov 2025 18:08:20 +0000 Received: by devbig002.atn3.facebook.com (Postfix, from userid 673679) id BC21BB794947; Wed, 12 Nov 2025 10:08:06 -0800 (PST) From: Emil Tsalapatis To: CC: , , , , Emil Tsalapatis , Emil Tsalapatis Subject: [PATCH] sched/ext: convert scx_tasks_lock to raw spinlock Date: Wed, 12 Nov 2025 10:07:55 -0800 Message-ID: <20251112180755.1701048-1-etsal@meta.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: sched-ext@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-GUID: 8gkHWxc2a6OokChU11xvWNb-eONAMMzr X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTEyMDE0NSBTYWx0ZWRfXw+A2oF9FxjvO kA8HXwjyjbwNejqODQTxM5TERzNSJgn62Eo3sOqo+x4hAXV5U9vS9VTC6pLos5x9UszLY89+CMe 7ggj0vtSdKF5gP9IFJyjXDPsLPrCqMCiltgbAOTO1/+vXTspb9cgOYOJZYrKCR6cq1d7JX1GUD8 RYhFpnHYbMoU/KmD8SpMUGSGCIF+XT/ZZjUA5PX5SNFHl7SsMKDyJB14DIM2EWAUOY8+hwrBZZK gsdsWvVXTS/Eno1PvItQZjSQx2/wGewEWlZWz1OIrh0Vm35vVSh71ts1c6fiWnZtaRl7XtHuHVs qVhTq4l8iseDDZT14lV/3W/MvcXl6GJbxlndGOKun8QQraJq9Pjq1D4rbQrlEGVrwyLhmRlGPQA xEvIxUrchlDIcvTLMLQD5YoIdBqK+g== X-Authority-Analysis: v=2.4 cv=Scv6t/Ru c=1 sm=1 tr=0 ts=6914cd23 cx=c_pps a=MfjaFnPeirRr97d5FC5oHw==:117 a=MfjaFnPeirRr97d5FC5oHw==:17 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=CWErhr8FAAAA:8 a=SUdZJXW00YaEYDIkTfgA:9 a=I-g_0vLIplkVOQ0FYkeP:22 X-Proofpoint-ORIG-GUID: 8gkHWxc2a6OokChU11xvWNb-eONAMMzr X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-12_06,2025-11-11_03,2025-10-01_01 Update scx_task_locks so that it's safe to lock/unlock in a non-sleepable context in PREEMPT_RT kernels. scx_task_locks is (non-raw) spinlock used to protect the list of tasks under SCX. This list is updated during from finish_task_switch(), which cannot sleep. Regular spinlocks can be locked in such a context in non-RT kernels, but are sleepable under when CONFIG_PREEMPT_RT=3Dy. Convert scx_task_locks into a raw spinlock, which is not sleepable even on RT kernels. Sample backtrace: dump_stack_lvl+0x83/0xa0 __might_resched+0x14a/0x200 rt_spin_lock+0x61/0x1c0 ? sched_ext_dead+0x2d/0xf0 ? lock_release+0xc6/0x280 sched_ext_dead+0x2d/0xf0 ? srso_alias_return_thunk+0x5/0xfbef5 finish_task_switch.isra.0+0x254/0x360 __schedule+0x584/0x11d0 ? srso_alias_return_thunk+0x5/0xfbef5 ? srso_alias_return_thunk+0x5/0xfbef5 ? tick_nohz_idle_exit+0x7e/0x120 schedule_idle+0x23/0x40 cpu_startup_entry+0x29/0x30 start_secondary+0xf8/0x100 common_startup_64+0x13e/0x148 Signed-off-by: Emil Tsalapatis --- kernel/sched/ext.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index bbd7529fa420..4b1007e06e9a 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -25,7 +25,7 @@ static struct scx_sched __rcu *scx_root; * guarantee system safety. Maintain a dedicated task list which contain= s every * task between its fork and eventual free. */ -static DEFINE_SPINLOCK(scx_tasks_lock); +static DEFINE_RAW_SPINLOCK(scx_tasks_lock); static LIST_HEAD(scx_tasks); =20 /* ops enable/disable */ @@ -520,7 +520,7 @@ static void scx_task_iter_start(struct scx_task_iter = *iter) { memset(iter, 0, sizeof(*iter)); =20 - spin_lock_irq(&scx_tasks_lock); + raw_spin_lock_irq(&scx_tasks_lock); =20 iter->cursor =3D (struct sched_ext_entity){ .flags =3D SCX_TASK_CURSOR = }; list_add(&iter->cursor.tasks_node, &scx_tasks); @@ -549,14 +549,14 @@ static void scx_task_iter_unlock(struct scx_task_it= er *iter) __scx_task_iter_rq_unlock(iter); if (iter->list_locked) { iter->list_locked =3D false; - spin_unlock_irq(&scx_tasks_lock); + raw_spin_unlock_irq(&scx_tasks_lock); } } =20 static void __scx_task_iter_maybe_relock(struct scx_task_iter *iter) { if (!iter->list_locked) { - spin_lock_irq(&scx_tasks_lock); + raw_spin_lock_irq(&scx_tasks_lock); iter->list_locked =3D true; } } @@ -2983,9 +2983,9 @@ void scx_post_fork(struct task_struct *p) } } =20 - spin_lock_irq(&scx_tasks_lock); + raw_spin_lock_irq(&scx_tasks_lock); list_add_tail(&p->scx.tasks_node, &scx_tasks); - spin_unlock_irq(&scx_tasks_lock); + raw_spin_unlock_irq(&scx_tasks_lock); =20 percpu_up_read(&scx_fork_rwsem); } @@ -3009,9 +3009,9 @@ void sched_ext_dead(struct task_struct *p) { unsigned long flags; =20 - spin_lock_irqsave(&scx_tasks_lock, flags); + raw_spin_lock_irqsave(&scx_tasks_lock, flags); list_del_init(&p->scx.tasks_node); - spin_unlock_irqrestore(&scx_tasks_lock, flags); + raw_spin_unlock_irqrestore(&scx_tasks_lock, flags); =20 /* * @p is off scx_tasks and wholly ours. scx_enable()'s READY -> ENABLED --=20 2.47.3