From patchwork Wed Nov 30 08:23:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 13059553 X-Patchwork-Delegate: bpf@iogearbox.net 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 A16B6C47088 for ; Wed, 30 Nov 2022 08:26:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235275AbiK3I0O (ORCPT ); Wed, 30 Nov 2022 03:26:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235069AbiK3IZX (ORCPT ); Wed, 30 Nov 2022 03:25:23 -0500 Received: from mail-pj1-x102a.google.com (mail-pj1-x102a.google.com [IPv6:2607:f8b0:4864:20::102a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 024DD6F807; Wed, 30 Nov 2022 00:24:18 -0800 (PST) Received: by mail-pj1-x102a.google.com with SMTP id t11-20020a17090a024b00b0021932afece4so1194547pje.5; Wed, 30 Nov 2022 00:24:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:sender:from:to:cc:subject:date :message-id:reply-to; bh=TeRxkUtMHLuUFqMgF18Iov3Mm0w03j8sOh2D0fkG7OA=; b=g9whwIlDXn1gAn57uP4ayQTIZ3MxO29p26WHIkTYhqXN0IbpiDCF+mEdhTWoghYZ8N OkxSP2pE6rvgdR/iELyZXC0pKsC6gJvixv940sey3X8shr915VlvYN1itzp6TzWEVwBY OHoHUn/0bPuL36ql//W3BHrB0hGaeLEQ1hD5qgVUtE8VNu20iu6LXQknEYuyGpZGF64X Qf+EYt5RYOgyePeftfpU9i+OmLjTkxFmq8D47KBfwzg3FQctawGt3Bm9pMD+4Kl4KJ+P rPC2ICIucZHJEDBGDV10EMeZhFyKssPlJ1/u5DRPr4s7h74HuEovmgSLGoBrI2ZVH5Qs 1Trg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:sender:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=TeRxkUtMHLuUFqMgF18Iov3Mm0w03j8sOh2D0fkG7OA=; b=Lz0i7nMPro+6SrOKGfjgZ9FnrLPrW6koqTip+3LCG5a4qGP6r4ltLGJa2mUwwpZ2Qc HA/tn7SV+2rWaHYF1Tayzs4tlgD3KyCHuECsyloiE4MXo+OneClJPfXXNJOwCJisHcNI HpsV+jO9Z0YvdHWv2fxBEogm7W9rHpGiH/ACSY/UG1iFyo12fwQkjg59zz4gF0JPWqjc DahIlQPR3NFSgVMQ3521CdiOhssjRrAST0obO5jltUwyGq76aSG90JTM783vbO6asob9 60lnDWImfmL4wj59CNnVFkRpbHieZRQqM6cRrMmvu+DJwifCgpINFk2Lt6iiRzIQCgKe XvPg== X-Gm-Message-State: ANoB5pkc53DxMTnGVOKXaDLitgYvdpmxGVIJ6iJ7D8HVPWPba1XTVLoL JV0Cp+RO1zc2Ux+9snSQSHg= X-Google-Smtp-Source: AA0mqf6mefq6GpDFMq05Kn+XBObUaj8OK0h0LXJbfOCd4ac/a8nw3NHFz5iV18RMVmHoXFAtXBm/VA== X-Received: by 2002:a17:90b:784:b0:218:fa11:5f87 with SMTP id l4-20020a17090b078400b00218fa115f87mr32105256pjz.25.1669796658265; Wed, 30 Nov 2022 00:24:18 -0800 (PST) Received: from localhost ([2600:380:4a00:1415:d028:b547:7d35:7b0b]) by smtp.gmail.com with ESMTPSA id f131-20020a623889000000b00574ebfdc721sm837329pfa.16.2022.11.30.00.24.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Nov 2022 00:24:17 -0800 (PST) Sender: Tejun Heo From: Tejun Heo To: torvalds@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com, brho@google.com, pjt@google.com, derkling@google.com, haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Tejun Heo Subject: [PATCH 19/31] sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT Date: Tue, 29 Nov 2022 22:23:01 -1000 Message-Id: <20221130082313.3241517-20-tj@kernel.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221130082313.3241517-1-tj@kernel.org> References: <20221130082313.3241517-1-tj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org BPF schedulers might not want to schedule certain tasks - e.g. kernel threads. This patch adds p->scx.disallow which can be set by BPF schedulers in such cases. The field can be changed anytime and setting it in ops.prep_enable() guarantees that the task can never be scheduled by sched_ext. scx_example_qmap is updated with the -d option to disallow a specific PID: # echo $$ 1092 # egrep '(policy)|(ext\.enabled)' /proc/self/sched policy : 0 ext.enabled : 0 # ./set-scx 1092 # egrep '(policy)|(ext\.enabled)' /proc/self/sched policy : 7 ext.enabled : 0 Run "scx_example_qmap -d 1092" in another terminal. # grep rejected /sys/kernel/debug/sched/ext nr_rejected : 1 # egrep '(policy)|(ext\.enabled)' /proc/self/sched policy : 0 ext.enabled : 0 # ./set-scx 1092 setparam failed for 1092 (Permission denied) Signed-off-by: Tejun Heo Suggested-by: Barret Rhoden Reviewed-by: David Vernet Acked-by: Josh Don Acked-by: Hao Luo Acked-by: Barret Rhoden --- include/linux/sched/ext.h | 12 ++++++++ kernel/sched/core.c | 4 +++ kernel/sched/ext.c | 38 ++++++++++++++++++++++++++ kernel/sched/ext.h | 3 ++ tools/sched_ext/scx_example_qmap.bpf.c | 4 +++ tools/sched_ext/scx_example_qmap.c | 8 +++++- 6 files changed, 68 insertions(+), 1 deletion(-) diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index 1a57945abea0..82dcbecfcfb9 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -397,6 +397,18 @@ struct sched_ext_entity { */ u64 slice; + /* + * If set, reject future sched_setscheduler(2) calls updating the policy + * to %SCHED_EXT with -%EACCES. + * + * If set from ops.prep_enable() and the task's policy is already + * %SCHED_EXT, which can happen while the BPF scheduler is being loaded + * or by inhering the parent's policy during fork, the task's policy is + * rejected and forcefully reverted to %SCHED_NORMAL. The number of such + * events are reported through /sys/kernel/debug/sched_ext::nr_rejected. + */ + bool disallow; /* reject switching into SCX */ + /* cold fields */ struct list_head tasks_node; }; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 39d9ccb64f40..3404277fed30 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7552,6 +7552,10 @@ static int __sched_setscheduler(struct task_struct *p, goto unlock; } + retval = scx_check_setscheduler(p, policy); + if (retval) + goto unlock; + /* * If not changing anything there's no need to proceed further, * but store a possible modification of reset_on_fork. diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 030175f2b1d6..ddd5aa4a8bca 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -1509,6 +1509,8 @@ static int scx_ops_prepare_task(struct task_struct *p, struct task_group *tg) WARN_ON_ONCE(p->scx.flags & SCX_TASK_OPS_PREPPED); + p->scx.disallow = false; + if (SCX_HAS_OP(prep_enable)) { struct scx_enable_args args = { }; @@ -1519,6 +1521,27 @@ static int scx_ops_prepare_task(struct task_struct *p, struct task_group *tg) } } + if (p->scx.disallow) { + struct rq *rq; + struct rq_flags rf; + + rq = task_rq_lock(p, &rf); + + /* + * We're either in fork or load path and @p->policy will be + * applied right after. Reverting @p->policy here and rejecting + * %SCHED_EXT transitions from scx_check_setscheduler() + * guarantees that if ops.prep_enable() sets @p->disallow, @p + * can never be in SCX. + */ + if (p->policy == SCHED_EXT) { + p->policy = SCHED_NORMAL; + atomic64_inc(&scx_nr_rejected); + } + + task_rq_unlock(rq, p, &rf); + } + p->scx.flags |= (SCX_TASK_OPS_PREPPED | SCX_TASK_WATCHDOG_RESET); return 0; } @@ -1664,6 +1687,18 @@ static void switching_to_scx(struct rq *rq, struct task_struct *p) static void check_preempt_curr_scx(struct rq *rq, struct task_struct *p,int wake_flags) {} static void switched_to_scx(struct rq *rq, struct task_struct *p) {} +int scx_check_setscheduler(struct task_struct *p, int policy) +{ + lockdep_assert_rq_held(task_rq(p)); + + /* if disallow, reject transitioning into SCX */ + if (scx_enabled() && READ_ONCE(p->scx.disallow) && + p->policy != policy && policy == SCHED_EXT) + return -EACCES; + + return 0; +} + /* * Omitted operations: * @@ -2367,6 +2402,9 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log, if (off >= offsetof(struct task_struct, scx.slice) && off + size <= offsetofend(struct task_struct, scx.slice)) return SCALAR_VALUE; + if (off >= offsetof(struct task_struct, scx.disallow) && + off + size <= offsetofend(struct task_struct, scx.disallow)) + return SCALAR_VALUE; } if (atype == BPF_READ) diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h index bda1d9c11486..0743a0536560 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -79,6 +79,7 @@ int scx_fork(struct task_struct *p); void scx_post_fork(struct task_struct *p); void scx_cancel_fork(struct task_struct *p); int balance_scx(struct rq *rq, struct task_struct *prev, struct rq_flags *rf); +int scx_check_setscheduler(struct task_struct *p, int policy); void init_sched_ext_class(void); __printf(2, 3) void scx_ops_error_type(enum scx_exit_type type, @@ -136,6 +137,8 @@ static inline void scx_post_fork(struct task_struct *p) {} static inline void scx_cancel_fork(struct task_struct *p) {} static inline int balance_scx(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) { return 0; } +static inline int scx_check_setscheduler(struct task_struct *p, + int policy) { return 0; } static inline void init_sched_ext_class(void) {} static inline void scx_notify_sched_tick(void) {} diff --git a/tools/sched_ext/scx_example_qmap.bpf.c b/tools/sched_ext/scx_example_qmap.bpf.c index 9e0b6519c8a4..b6febc5dadbf 100644 --- a/tools/sched_ext/scx_example_qmap.bpf.c +++ b/tools/sched_ext/scx_example_qmap.bpf.c @@ -24,6 +24,7 @@ char _license[] SEC("license") = "GPL"; const volatile u64 slice_ns = SCX_SLICE_DFL; const volatile u32 stall_user_nth; const volatile u32 stall_kernel_nth; +const volatile s32 disallow_tgid; u32 test_error_cnt; @@ -208,6 +209,9 @@ void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev) s32 BPF_STRUCT_OPS(qmap_prep_enable, struct task_struct *p, struct scx_enable_args *args) { + if (p->tgid == disallow_tgid) + p->scx.disallow = true; + /* * @p is new. Let's ensure that its task_ctx is available. We can sleep * in this function and the following will automatically use GFP_KERNEL. diff --git a/tools/sched_ext/scx_example_qmap.c b/tools/sched_ext/scx_example_qmap.c index 34c764c38e19..99cc7169bd90 100644 --- a/tools/sched_ext/scx_example_qmap.c +++ b/tools/sched_ext/scx_example_qmap.c @@ -20,12 +20,13 @@ const char help_fmt[] = "\n" "See the top-level comment in .bpf.c for more details.\n" "\n" -"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT]\n" +"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-d PID]\n" "\n" " -s SLICE_US Override slice duration\n" " -e COUNT Trigger scx_bpf_error() after COUNT enqueues\n" " -t COUNT Stall every COUNT'th user thread\n" " -T COUNT Stall every COUNT'th kernel thread\n" +" -d PID Disallow a process from switching into SCHED_EXT (-1 for self)\n" " -h Display this help and exit\n"; static volatile int exit_req; @@ -63,6 +64,11 @@ int main(int argc, char **argv) case 'T': skel->rodata->stall_kernel_nth = strtoul(optarg, NULL, 0); break; + case 'd': + skel->rodata->disallow_tgid = strtol(optarg, NULL, 0); + if (skel->rodata->disallow_tgid < 0) + skel->rodata->disallow_tgid = getpid(); + break; default: fprintf(stderr, help_fmt, basename(argv[0])); return opt != 'h';