From nobody Fri Oct 3 07:42:40 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 21FCB2EBBA8 for ; Wed, 3 Sep 2025 21:23:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756934614; cv=none; b=eXEH+NJEDgeEkISyJ22eMJDe1NansNvCMH6Arf7ni7K/XVX7wUBPNLdynKveiywku3Sb+nj2UZeTqAkrI9bSYmszFZ5ZQzsbR0zstCR6OLmqEEVsbIB2uYTPES1bpLJKpjOz5Zwcms+b1rK7y5XKbS7z0C/8oVp8QoYBJGAhVHs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756934614; c=relaxed/simple; bh=B5JeQxB0xaaKDctXaK8S+6y0REKZuDCZibWyVPtHdCw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=UxYI9YNlK+PVELrqdmSgyFdyu8CCOFfAo7pUw//E/djX/U8CeZunK1neYYXZbZUylNQkGqi0gxJ09sz433DNnfoX81vlJruSyNnCCG67IowSJyUyDrEpigd52l17YQ9nbQeguD4FzhVHIatbhVakEZ6Fy2ZzJzNWlyxwTJu6mXw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 315E51688; Wed, 3 Sep 2025 14:23:24 -0700 (PDT) Received: from e127648.arm.com (unknown [10.57.93.203]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id B1A973F694; Wed, 3 Sep 2025 14:23:30 -0700 (PDT) From: Christian Loehle To: tj@kernel.org, arighi@nvidia.com, void@manifault.com Cc: linux-kernel@vger.kernel.org, sched-ext@lists.linux.dev, changwoo@igalia.com, hodgesd@meta.com, mingo@redhat.com, peterz@infradead.org, jake@hillion.co.uk, Christian Loehle Subject: [PATCH v7 1/3] sched_ext: Introduce scx_bpf_locked_rq() Date: Wed, 3 Sep 2025 22:23:09 +0100 Message-Id: <20250903212311.369697-2-christian.loehle@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250903212311.369697-1-christian.loehle@arm.com> References: <20250903212311.369697-1-christian.loehle@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Most fields in scx_bpf_cpu_rq() assume that its rq_lock is held. Furthermore they become meaningless without rq lock, too. Make a safer version of scx_bpf_cpu_rq() that only returns a rq if we hold rq lock of that rq. Also mark the new scx_bpf_locked_rq() as returning NULL as scx_bpf_cpu_rq() should've been too. Signed-off-by: Christian Loehle Acked-by: Andrea Righi --- kernel/sched/ext.c | 23 +++++++++++++++++++++++ tools/sched_ext/include/scx/common.bpf.h | 1 + 2 files changed, 24 insertions(+) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 4ae32ef179dd..e15f1b0501a1 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -7430,6 +7430,28 @@ __bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu) return cpu_rq(cpu); } =20 +/** + * scx_bpf_locked_rq - Return the rq currently locked by SCX + * + * Returns the rq if a rq lock is currently held by SCX. + * Otherwise emits an error and returns NULL. + */ +__bpf_kfunc struct rq *scx_bpf_locked_rq(void) +{ + struct rq *rq; + + preempt_disable(); + rq =3D scx_locked_rq(); + if (!rq) { + preempt_enable(); + scx_kf_error("accessing rq without holding rq lock"); + return NULL; + } + preempt_enable(); + + return rq; +} + /** * scx_bpf_task_cgroup - Return the sched cgroup of a task * @p: task of interest @@ -7594,6 +7616,7 @@ BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_cpu_rq) +BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL) #ifdef CONFIG_CGROUP_SCHED BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_RCU | KF_ACQUIRE) #endif diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/inc= lude/scx/common.bpf.h index d4e21558e982..e9b006226cf6 100644 --- a/tools/sched_ext/include/scx/common.bpf.h +++ b/tools/sched_ext/include/scx/common.bpf.h @@ -91,6 +91,7 @@ s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u= 64 flags) __ksym; bool scx_bpf_task_running(const struct task_struct *p) __ksym; s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym; struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym; +struct rq *scx_bpf_locked_rq(void) __ksym; struct cgroup *scx_bpf_task_cgroup(struct task_struct *p) __ksym __weak; u64 scx_bpf_now(void) __ksym __weak; void scx_bpf_events(struct scx_event_stats *events, size_t events__sz) __k= sym __weak; --=20 2.34.1 From nobody Fri Oct 3 07:42:40 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 46C712EB85A for ; Wed, 3 Sep 2025 21:23:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756934616; cv=none; b=OkgzBygC4uHXlobanPa3SXykaPpKsR3S+RUhdJUd4slC0IsOIseKtK15JQjdnMYD4Nl2mjlfpTiMpJZd66aIDEOIHFPmupyVZDFzOyBPbGw3kts+33rgJ2VfhHGC3zDuxlma3Fd1wu4yhwqvdXmYy4/aR4tFz4FL7UE9qqBipDE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756934616; c=relaxed/simple; bh=E94B3/I+ey8U/6ABm8kiPpbbVtCdMVHMMGK9O95zHXI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=FikLaCI4SX6e/0rIPgqXGIv3XEVumb4N6ItEUXumG12ZOPLX7phyhbSlghJbYO1yUzjEwuT4JGvHLDs574IG1xU2z+2ZUfASHDm19LbtcQkKVaUxYalok46tTWnc7TRBW7bbkXHgIWkpj4BuBMVAhD8dVrcEZ9w/wzH8Y+G/T0c= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 55AAB1BD0; Wed, 3 Sep 2025 14:23:26 -0700 (PDT) Received: from e127648.arm.com (unknown [10.57.93.203]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id D6A8B3F694; Wed, 3 Sep 2025 14:23:32 -0700 (PDT) From: Christian Loehle To: tj@kernel.org, arighi@nvidia.com, void@manifault.com Cc: linux-kernel@vger.kernel.org, sched-ext@lists.linux.dev, changwoo@igalia.com, hodgesd@meta.com, mingo@redhat.com, peterz@infradead.org, jake@hillion.co.uk, Christian Loehle Subject: [PATCH v7 2/3] sched_ext: Introduce scx_bpf_cpu_curr() Date: Wed, 3 Sep 2025 22:23:10 +0100 Message-Id: <20250903212311.369697-3-christian.loehle@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250903212311.369697-1-christian.loehle@arm.com> References: <20250903212311.369697-1-christian.loehle@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Provide scx_bpf_cpu_curr() as a way for scx schedulers to check the curr task of a remote rq without assuming its lock is held. Many scx schedulers make use of scx_bpf_cpu_rq() to check a remote curr (e.g. to see if it should be preempted). This is problematic because scx_bpf_cpu_rq() provides access to all fields of struct rq, most of which aren't safe to use without holding the associated rq lock. Signed-off-by: Christian Loehle Acked-by: Andrea Righi --- kernel/sched/ext.c | 14 ++++++++++++++ tools/sched_ext/include/scx/common.bpf.h | 1 + 2 files changed, 15 insertions(+) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index e15f1b0501a1..6ea81b6a6b2d 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -7452,6 +7452,19 @@ __bpf_kfunc struct rq *scx_bpf_locked_rq(void) return rq; } +/** + * scx_bpf_cpu_curr - Return remote CPU's curr task + * @cpu: CPU of interest + * + * Callers must hold RCU read lock (KF_RCU). + */ +__bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu) +{ + if (!kf_cpu_valid(cpu, NULL)) + return NULL; + return rcu_dereference(cpu_rq(cpu)->curr); +} + /** * scx_bpf_task_cgroup - Return the sched cgroup of a task * @p: task of interest @@ -7617,6 +7630,7 @@ BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_cpu_rq) BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL) +BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_RET_NULL | KF_RCU) #ifdef CONFIG_CGROUP_SCHED BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_RCU | KF_ACQUIRE) #endif diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/inc= lude/scx/common.bpf.h index e9b006226cf6..03e614506fa3 100644 --- a/tools/sched_ext/include/scx/common.bpf.h +++ b/tools/sched_ext/include/scx/common.bpf.h @@ -92,6 +92,7 @@ bool scx_bpf_task_running(const struct task_struct *p) __= ksym; s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym; struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym; struct rq *scx_bpf_locked_rq(void) __ksym; +struct task_struct *scx_bpf_cpu_curr(s32 cpu) __ksym; struct cgroup *scx_bpf_task_cgroup(struct task_struct *p) __ksym __weak; u64 scx_bpf_now(void) __ksym __weak; void scx_bpf_events(struct scx_event_stats *events, size_t events__sz) __k= sym __weak; -- 2.34.1 From nobody Fri Oct 3 07:42:40 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7045A2EC573 for ; Wed, 3 Sep 2025 21:23:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756934619; cv=none; b=MFiqulw2A6z9969l1iGB5tZiSplRPovSHpZcil762ev4KLcQV30xgwxCzWINNucM0lKYiNztcZ4orfvKVJxny04FBIjzlZBPJrhJpAuo1nwLHjATHKoEZ1C5q1ojTj8fma2masyOYL3LDrOsYpjUEVT00LkJgfqRVrejKUPdrgo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756934619; c=relaxed/simple; bh=ElRvS8XUhRJeZToccc++Fe/3u4yPQ0/w/ug2DD+z+Xg=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=VuJ9memuufg6UmlozL29eVm1KKBeFWvO1wjYEDiU6erdMJpg213Wf9GdqIjonJu+kvu0Kv8GaN4RiGA8Tgp0jHU7s9QfV18X9KOIy1UUv0Zp3uXUmwUJTBLMW3JrxZCnYXF9MLZJkDWYf7kAvl3ZuIhqFzIckw/PEED7v55afds= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7E0421CE0; Wed, 3 Sep 2025 14:23:28 -0700 (PDT) Received: from e127648.arm.com (unknown [10.57.93.203]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 044C23F694; Wed, 3 Sep 2025 14:23:34 -0700 (PDT) From: Christian Loehle To: tj@kernel.org, arighi@nvidia.com, void@manifault.com Cc: linux-kernel@vger.kernel.org, sched-ext@lists.linux.dev, changwoo@igalia.com, hodgesd@meta.com, mingo@redhat.com, peterz@infradead.org, jake@hillion.co.uk, Christian Loehle Subject: [PATCH v7 3/3] sched_ext: deprecation warn for scx_bpf_cpu_rq() Date: Wed, 3 Sep 2025 22:23:11 +0100 Message-Id: <20250903212311.369697-4-christian.loehle@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250903212311.369697-1-christian.loehle@arm.com> References: <20250903212311.369697-1-christian.loehle@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" scx_bpf_cpu_rq() works on an unlocked rq which generally isn't safe. For the common use-cases scx_bpf_locked_rq() and scx_bpf_cpu_curr() work, so add a deprecation warning to scx_bpf_cpu_rq() so it can eventually be removed. Signed-off-by: Christian Loehle --- kernel/sched/ext.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 6ea81b6a6b2d..1a0afdf5fcf5 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -873,6 +873,7 @@ struct scx_sched { struct scx_event_stats __percpu *event_stats_cpu; =20 bool warned_zero_slice; + bool warned_deprecated_rq; =20 atomic_t exit_kind; struct scx_exit_info *exit_info; @@ -7424,9 +7425,18 @@ __bpf_kfunc s32 scx_bpf_task_cpu(const struct task_s= truct *p) */ __bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu) { + struct scx_sched *sch =3D scx_root; + if (!kf_cpu_valid(cpu, NULL)) return NULL; =20 + if (!sch->warned_deprecated_rq) { + printk_deferred(KERN_WARNING "sched_ext: %s() is deprecated; " + "use scx_bpf_locked_rq() when holding rq lock " + "or scx_bpf_cpu_curr() to read remote curr safely.\n", __func__); + sch->warned_deprecated_rq =3D true; + } + return cpu_rq(cpu); } =20 --=20 2.34.1