From patchwork Tue Jun 18 21:17:28 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 13703049 Received: from mail-pf1-f182.google.com (mail-pf1-f182.google.com [209.85.210.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E94517966F; Tue, 18 Jun 2024 21:21:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.182 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718745693; cv=none; b=EuZo/d/3G0Weo0M0+W4RE3cmYGJD84Kyr7wdSzlB17F5cEHx2qjO/qaxFkj/2sewd7+p+OS4yy/+F+Qd5j7OUZUwAsgrKI9BtlYK8ki/B9Gx0TecliJzalzGyYpZKmhcVWG4G77G9EpRP0bJq5Dr70WVvdeXoGFPXkKLdcIXAH8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718745693; c=relaxed/simple; bh=NVtuhmD5qkkKR8hTFNL9KWL3HrWGAH/j+eE1vG9vbUw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=elV2c2IAhBTzMpXL527bE0QcsOzQpNAVgPWQe3ghU5AkgVjydtu1T3bLGh1oe+q1fg8Z3gj1bX2SSbBzV0W8d820Ix6W6ULn4ST0Yjl8sYIuSc6AdbbxNy3NDGxwcFlbNnghs9zW7Qi6lH1ZoYXcgW+llOn96eyz/xyMyyxpwJs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=fk5bEBAp; arc=none smtp.client-ip=209.85.210.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="fk5bEBAp" Received: by mail-pf1-f182.google.com with SMTP id d2e1a72fcca58-7046211e455so4271386b3a.3; Tue, 18 Jun 2024 14:21:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1718745690; x=1719350490; 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=eheGkzhhj7NDyOhT2V44W7D5tLTQgeESmDFvuhj5/IU=; b=fk5bEBApi4eSfWqTh6t1hBNqZMBc5d+FYVPKPyiixuNeht+/sF2w6yKEtJ0mAABJ3C ovuNT4Eu82W+7z3EJdGGnb5MdB6npDPYox0cKGxdj3YgKjXmenSF5t2/fJe+ZYpQTAod eL3x5Tn1xQj+2bzdCrn6H0pWKawW5sRlPtXEz342vcukz6N4Z3qiKEtjZ/q/7TQOm5l+ 2G65MJMWseNGXraufEuVkK6aenWWsLzwqqJkAvt8jZcZD0k/nx0h2Jn8Ue+W6hwiZHCl UPTj/+ZHpRokh9KYcMQFn/inf4r+w6qvZwODzAcPnZzwlJHzYmIjJbEA1Z9dEmNqaMNd h5Vg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1718745690; x=1719350490; 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=eheGkzhhj7NDyOhT2V44W7D5tLTQgeESmDFvuhj5/IU=; b=fwAr2TqJIl0WDsZBRV78tfPz5wEwbxAhmClkwC4URva0nFZejadksVN8NS24xsdI1k 3R1WwotxnoYD1pjKRaxjnlg7pHi7JsC8ba7/Bo/06aHN5Zx3ULzz2xSwV08fX9il1pp4 bVsaDmqiIPuygdqHxG000yfLKWDab5zeiHSACsp+pUsWQlUWGbkxtG7L41UtxYCKQlyN viaXCmxHGa/Y3nlO3YntQNsdYdkDfOL3wfo0BM/6MRbk+ra0S84eqJinKSjB3uyQcPAe xrC8GQEgVsvvjleg3IVou8k8bAwPLiUEt6jiDHNAG1AfwGrIrQ4jDJd6DBGoguJu+WEv slwQ== X-Forwarded-Encrypted: i=1; AJvYcCVDqMeZ6COrO6Rq4NltcxWXPvjp4AcD2CQSK2pjYR3cFRiIR78H0jknIHf38vdWF7Uw9Q7DZu8d3XOGCBXMnOe6mvud X-Gm-Message-State: AOJu0YyIQ9iknIwSw0+KAbouacyP5/khSlU140rgzuJ1KzO/ikqdsOdD C0DP3AMI+1yF4UkC3bQwvBc8Fway64u9PVSYuqGnyQ+bKHR4ibl7 X-Google-Smtp-Source: AGHT+IHRwmUnVWieA+HPqeMA94SH8RdY3DxBQ+/P8duoVnXwbfUZkxqJQrJsLd2I7Qe24MwILuaeYg== X-Received: by 2002:a17:90a:c682:b0:2c3:1937:3042 with SMTP id 98e67ed59e1d1-2c7b59fa634mr922325a91.5.1718745689797; Tue, 18 Jun 2024 14:21:29 -0700 (PDT) Received: from localhost (dhcp-141-239-159-203.hawaiiantel.net. [141.239.159.203]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2c4c45f68e4sm11370657a91.28.2024.06.18.14.21.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Jun 2024 14:21:29 -0700 (PDT) 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, andrea.righi@canonical.com, joel@joelfernandes.org Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Tejun Heo Subject: [PATCH 13/30] sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT Date: Tue, 18 Jun 2024 11:17:28 -1000 Message-ID: <20240618212056.2833381-14-tj@kernel.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240618212056.2833381-1-tj@kernel.org> References: <20240618212056.2833381-1-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 # grep -E '(policy)|(ext\.enabled)' /proc/self/sched policy : 0 ext.enabled : 0 # ./set-scx 1092 # grep -E '(policy)|(ext\.enabled)' /proc/self/sched policy : 7 ext.enabled : 0 Run "scx_qmap -p -d 1092" in another terminal. # cat /sys/kernel/sched_ext/nr_rejected 1 # grep -E '(policy)|(ext\.enabled)' /proc/self/sched policy : 0 ext.enabled : 0 # ./set-scx 1092 setparam failed for 1092 (Permission denied) - v4: Refreshed on top of tip:sched/core. - v3: Update description to reflect /sys/kernel/sched_ext interface change. - 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/ext.c | 50 ++++++++++++++++++++++++++++++++++ kernel/sched/ext.h | 2 ++ kernel/sched/syscalls.c | 4 +++ tools/sched_ext/scx_qmap.bpf.c | 4 +++ tools/sched_ext/scx_qmap.c | 11 ++++++-- 6 files changed, 81 insertions(+), 2 deletions(-) diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index 96031252436f..ea7c501ac819 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -137,6 +137,18 @@ 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.init_task() 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 */ /* must be the last field, see init_scx_entity() */ struct list_head tasks_node; diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 3dc515b3351f..8ff30b80e862 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -483,6 +483,8 @@ struct static_key_false scx_has_op[SCX_OPI_END] = 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 @@ -2332,6 +2334,8 @@ static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool { int ret; + p->scx.disallow = false; + if (SCX_HAS_OP(init_task)) { struct scx_init_task_args args = { .fork = fork, @@ -2346,6 +2350,27 @@ static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool scx_set_task_state(p, SCX_TASK_INIT); + 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.init_task() 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_RESET_RUNNABLE_AT; return 0; } @@ -2549,6 +2574,18 @@ static void switched_from_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: * @@ -2703,9 +2740,17 @@ static ssize_t scx_attr_switch_all_show(struct kobject *kobj, } SCX_ATTR(switch_all); +static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_nr_rejected)); +} +SCX_ATTR(nr_rejected); + static struct attribute *scx_global_attrs[] = { &scx_attr_state.attr, &scx_attr_switch_all.attr, + &scx_attr_nr_rejected.attr, NULL, }; @@ -3178,6 +3223,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link) 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(). @@ -3476,6 +3523,9 @@ 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 56fcdb0b2c05..33a9f7fe5832 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -35,6 +35,7 @@ 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); bool task_should_scx(struct task_struct *p); void init_sched_ext_class(void); @@ -72,6 +73,7 @@ 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 bool task_on_scx(const struct task_struct *p) { return false; } static inline void init_sched_ext_class(void) {} diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index 18d44d180db1..4fa59c9f69ac 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -714,6 +714,10 @@ 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/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c index 8beae08dfdc7..5ff217c4bfa0 100644 --- a/tools/sched_ext/scx_qmap.bpf.c +++ b/tools/sched_ext/scx_qmap.bpf.c @@ -32,6 +32,7 @@ const volatile u64 slice_ns = SCX_SLICE_DFL; const volatile u32 stall_user_nth; const volatile u32 stall_kernel_nth; const volatile u32 dsp_batch; +const volatile s32 disallow_tgid; u32 test_error_cnt; @@ -243,6 +244,9 @@ void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev) s32 BPF_STRUCT_OPS(qmap_init_task, struct task_struct *p, struct scx_init_task_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 6e9e9726cd62..a2614994cfaa 100644 --- a/tools/sched_ext/scx_qmap.c +++ b/tools/sched_ext/scx_qmap.c @@ -19,13 +19,15 @@ 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] [-b COUNT] [-p] [-v]\n" +"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-b COUNT]\n" +" [-d PID] [-p] [-v]\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" " -b COUNT Dispatch upto COUNT tasks together\n" +" -d PID Disallow a process from switching into SCHED_EXT (-1 for self)\n" " -p Switch only tasks on SCHED_EXT policy intead of all\n" " -v Print libbpf debug messages\n" " -h Display this help and exit\n"; @@ -57,7 +59,7 @@ int main(int argc, char **argv) skel = SCX_OPS_OPEN(qmap_ops, scx_qmap); - while ((opt = getopt(argc, argv, "s:e:t:T:b:pvh")) != -1) { + while ((opt = getopt(argc, argv, "s:e:t:T:b:d:pvh")) != -1) { switch (opt) { case 's': skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000; @@ -74,6 +76,11 @@ int main(int argc, char **argv) case 'b': skel->rodata->dsp_batch = 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; case 'p': skel->struct_ops.qmap_ops->flags |= SCX_OPS_SWITCH_PARTIAL; break;