From patchwork Sat Nov 11 02:47:42 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 13452940 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 7C87615B8 for ; Sat, 11 Nov 2023 02:51:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="E5VnCXzx" Received: from mail-oa1-x2e.google.com (mail-oa1-x2e.google.com [IPv6:2001:4860:4864:20::2e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF5C64C27; Fri, 10 Nov 2023 18:49:27 -0800 (PST) Received: by mail-oa1-x2e.google.com with SMTP id 586e51a60fabf-1f055438492so1511563fac.3; Fri, 10 Nov 2023 18:49:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1699670966; x=1700275766; darn=vger.kernel.org; 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=VbJyk8Se0g0ZLIJL7NAOIYPUw+pRNH8PHA5+GCmAHCE=; b=E5VnCXzx2NCfxv4HWLmpbD5HKSwTD5SzruFj5ceFdrVQt76Wer8tapXJw8p1hiaGWI gYeGcWWAsC75SPXeloNReamEelw9j+UUgWTgcI5KLc4JLexOLGILEBugs9TgKAly5e6y 60fhY4tcBmKZJZH41E7KuO2YBrKX8qhBZgi7UtMVoMZvs68NVjucQbdmoN6sylA84RXM OeGqL5fpOtCf7EVY7hbw5aInZAtegq7MB1IqZQ1tPhxRMxdyBTbtLXlsVav6hbjtW39L 89shFCYAB2qTa1igCflJb2n6KcTh6xroL6FYVbhmC0a8GhYQ2iOw+AGCgxjISiNM6d8o cyZQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699670966; x=1700275766; 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=VbJyk8Se0g0ZLIJL7NAOIYPUw+pRNH8PHA5+GCmAHCE=; b=ToSpup2dQgcd2N+lwnwp7G2lB2TXACybpul/noLHIbEHg7m95Q+EJF61CsJbN16LvW uNPlEebr4ODkjiQ734KvG7ExXAW++QkL9Xlm0AQpygvHbjsaq+ufPuZpjBG/JO4vA+Qz A38Q0jEw3iIE8QgYGj52ZrvwikfKgnVZ3r2QrTVjm07LvIeD5NLA7JpCV+0zy6TMVVRd 4IqfYb9qDVx2N+HsvvnFnKUo6803IpzFBi4bvqQgJ7XO34r6w/uaUcVvQLOmPiNaCQ32 28cQKG3bDO3rO3e1THjl7oLoI0ybDSZJlkdZiGhUvERd5SaZQUZVFtZRTMhFUboVDMyD 7RUA== X-Gm-Message-State: AOJu0Yyf9/AEmTYWvUWfrhoveUDVlmslb01GLBcOJXpynKQCPurMKRhq aL7dVW4v4erpFeuzfCIUI8E= X-Google-Smtp-Source: AGHT+IGKykYwZ5Y2H8QB+C93WxjNufePRhpo0JvnLzoUlprAjCqO9FiU0OTvJBY7y2Sliv3dfr85jA== X-Received: by 2002:a05:6871:4509:b0:1ea:137:7dba with SMTP id nj9-20020a056871450900b001ea01377dbamr1444135oab.10.1699670966128; Fri, 10 Nov 2023 18:49:26 -0800 (PST) Received: from localhost ([2620:10d:c090:400::4:7384]) by smtp.gmail.com with ESMTPSA id s20-20020a62e714000000b006bc3e8f58besm396702pfh.56.2023.11.10.18.49.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Nov 2023 18:49:25 -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, changwoo@igalia.com, himadrics@inria.fr, memxor@gmail.com Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Tejun Heo Subject: [PATCH 16/36] sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT Date: Fri, 10 Nov 2023 16:47:42 -1000 Message-ID: <20231111024835.2164816-17-tj@kernel.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231111024835.2164816-1-tj@kernel.org> References: <20231111024835.2164816-1-tj@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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_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_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) * v2: Use atomic_long_t instead of atomic64_t for scx_kick_cpus_pnt_seqs to accommodate 32bit archs. 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 | 44 ++++++++++++++++++++++++++++++++++ kernel/sched/ext.h | 3 +++ tools/sched_ext/scx_qmap.bpf.c | 4 ++++ tools/sched_ext/scx_qmap.c | 8 ++++++- 6 files changed, 74 insertions(+), 1 deletion(-) diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index ec85415431d9..9d41acaf89c0 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -411,6 +411,18 @@ 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 c2ce0e8ac407..6b8883fedf33 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7809,6 +7809,10 @@ 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 37a0f9c148d9..025b6103b87d 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -93,6 +93,8 @@ struct static_key_false scx_has_op[SCX_NR_ONLINE_OPS] = static atomic_t scx_exit_kind = ATOMIC_INIT(SCX_EXIT_DONE); static struct scx_exit_info scx_exit_info; +static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0); + /* * The maximum amount of time in jiffies that a task may be runnable without * being scheduled on a CPU. If this timeout is exceeded, it will trigger @@ -1725,6 +1727,8 @@ 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 = { }; @@ -1735,6 +1739,27 @@ 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; + atomic_long_inc(&scx_nr_rejected); + } + + task_rq_unlock(rq, p, &rf); + } + p->scx.flags |= (SCX_TASK_OPS_PREPPED | SCX_TASK_WATCHDOG_RESET); return 0; } @@ -1896,6 +1921,18 @@ static void switching_to_scx(struct rq *rq, struct task_struct *p) static void wakeup_preempt_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: * @@ -2333,6 +2370,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops) atomic_set(&scx_exit_kind, SCX_EXIT_NONE); scx_warned_zero_slice = false; + atomic_long_set(&scx_nr_rejected, 0); + /* * Keep CPUs stable during enable so that the BPF scheduler can track * online CPUs by watching ->on/offline_cpu() after ->init(). @@ -2521,6 +2560,8 @@ static int scx_debug_show(struct seq_file *m, void *v) seq_printf(m, "%-30s: %ld\n", "enabled", scx_enabled()); seq_printf(m, "%-30s: %s\n", "enable_state", scx_ops_enable_state_str[scx_ops_enable_state()]); + seq_printf(m, "%-30s: %lu\n", "nr_rejected", + atomic_long_read(&scx_nr_rejected)); mutex_unlock(&scx_ops_enable_mutex); return 0; } @@ -2574,6 +2615,9 @@ 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; } return -EACCES; diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h index c4da4e2838fd..bd283ee54da7 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -87,6 +87,7 @@ void scx_pre_fork(struct task_struct *p); int scx_fork(struct task_struct *p); void scx_post_fork(struct task_struct *p); void scx_cancel_fork(struct task_struct *p); +int scx_check_setscheduler(struct task_struct *p, int policy); void init_sched_ext_class(void); __printf(2, 3) void scx_ops_error_kind(enum scx_exit_kind kind, @@ -142,6 +143,8 @@ static inline void scx_pre_fork(struct task_struct *p) {} static inline int scx_fork(struct task_struct *p) { return 0; } static inline void scx_post_fork(struct task_struct *p) {} static inline void scx_cancel_fork(struct task_struct *p) {} +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_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c index a1bdb5774a63..d0bc67095062 100644 --- a/tools/sched_ext/scx_qmap.bpf.c +++ b/tools/sched_ext/scx_qmap.bpf.c @@ -27,6 +27,7 @@ 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; @@ -224,6 +225,9 @@ 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_qmap.c b/tools/sched_ext/scx_qmap.c index 711827b38578..6002cef833ab 100644 --- a/tools/sched_ext/scx_qmap.c +++ b/tools/sched_ext/scx_qmap.c @@ -18,12 +18,13 @@ 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; @@ -61,6 +62,11 @@ 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';