From nobody Wed Oct 1 22:33:22 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 71470306D40; Wed, 1 Oct 2025 14:48:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759330122; cv=none; b=YBHC3Z3lNul/umJy1z72zCA6m8Ra5eDtNbqhtJZFxehCQVYcrAlxd9tMswtgzI8hnFXTLlGWp2ekEgnx0Cza5VwKSIIqKf27kPOCE0KsH7wdMfzUUpi0eTcjvzK9myblUwP+3XCIWfQLFyx7KpTksjCDtsoIvr8yqBIUrRFDS48= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759330122; c=relaxed/simple; bh=h25HXfqFwZPbzPp+0/q7PleMKwW/TXZPNmjI5yN4W8Q=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=gaJCUtoDYHc0XdbY9Y4ZCvjtiVYzx64nx021rOtcyIUGp7LVfOZZaoASkTvn/xAHYoOWMd/YGB/R5fAEv+ZUGMzbDhL5I55hkaiYN16NGVldJfYgLcsxD5IHLvUrVSanRt+3omJKksBGBWXKFHDXMVUgAke4tmylDcAQ1Zth7Rk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iLCIQ08z; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iLCIQ08z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0CD0FC4CEFB; Wed, 1 Oct 2025 14:48:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759330122; bh=h25HXfqFwZPbzPp+0/q7PleMKwW/TXZPNmjI5yN4W8Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iLCIQ08z3SlN2WlN4vUVtl0nuhTVvrV6DT78yaGGwFs4MPshPJxuGtQj6Gq10iJT0 A1yZ5/WwCHq1YysHhe7ZR7AgGHW0kJWhjwdm9okrAusdn8p9Lhr29gfoEWcJfjUgxk W3Nla37WhiWgfAetAal7z0U9dVmANGuAM8U1PvLe+tZ9QRqTqw2k3cSd0u0VPocQqI UeWIAv99XsjEzka5J3ywtxg7eJaAWSNraittJN32vWVGtTY7h06v5vTgOjdmWhDAVb 9ukKfRjbrpH4n+/w4p26/3XBglI2KoC4P3F7AOSBUEcXkQQEPtV51MjPc6Znfz/dTM PJcVvAI41/o8Q== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 8F63FCE14F4; Wed, 1 Oct 2025 07:48:34 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" , Mathieu Desnoyers , Sebastian Andrzej Siewior , bpf@vger.kernel.org Subject: [PATCH v2 18/21] srcu: Make SRCU-fast readers enforce use of SRCU-fast definition/init Date: Wed, 1 Oct 2025 07:48:29 -0700 Message-Id: <20251001144832.631770-18-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <7fa58961-2dce-4e08-8174-1d1cc592210f@paulmck-laptop> References: <7fa58961-2dce-4e08-8174-1d1cc592210f@paulmck-laptop> 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" This commit makes CONFIG_PROVE_RCU=3Dy kernels enforce the new rule that srcu_struct structures that are passed to srcu_read_lock_fast() and other SRCU-fast read-side markers be either initialized with init_srcu_struct_fast() on the one hand or defined with DEFINE_SRCU_FAST() or DEFINE_STATIC_SRCU_FAST() on the other. This eliminates the read-side test that was formerly included in srcu_read_lock_fast() and friends, speeding these primitives up by about 25% (admittedly only about half of a nanosecond, but when tracing on fastpaths...) Signed-off-by: Paul E. McKenney Cc: Mathieu Desnoyers Cc: Steven Rostedt Cc: Sebastian Andrzej Siewior Cc: --- include/linux/srcu.h | 6 +++--- include/linux/srcutiny.h | 1 - include/linux/srcutree.h | 16 +--------------- kernel/rcu/tasks.h | 5 ----- 4 files changed, 4 insertions(+), 24 deletions(-) diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 2982b5a6930fa6..41e27c1d917d3e 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -297,7 +297,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_= fast(struct srcu_struct * struct srcu_ctr __percpu *retval; =20 RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock= _fast()."); - srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST); + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST); retval =3D __srcu_read_lock_fast(ssp); rcu_try_lock_acquire(&ssp->dep_map); return retval; @@ -312,7 +312,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_= fast_notrace(struct srcu_ { struct srcu_ctr __percpu *retval; =20 - srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST); + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST); retval =3D __srcu_read_lock_fast(ssp); return retval; } @@ -333,7 +333,7 @@ static inline struct srcu_ctr __percpu *srcu_down_read_= fast(struct srcu_struct * { WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi()); RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_down_read= _fast()."); - srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST); + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST); return __srcu_read_lock_fast(ssp); } =20 diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index 92e6ab53398fc0..1ecc3393fb26be 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -112,7 +112,6 @@ static inline void srcu_barrier(struct srcu_struct *ssp) =20 static inline void srcu_expedite_current(struct srcu_struct *ssp) { } #define srcu_check_read_flavor(ssp, read_flavor) do { } while (0) -#define srcu_check_read_flavor_force(ssp, read_flavor) do { } while (0) =20 /* Defined here to avoid size increase for non-torture kernels. */ static inline void srcu_torture_stats_print(struct srcu_struct *ssp, diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 05400f70baa40a..fd24ec146af614 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -311,21 +311,7 @@ __srcu_read_unlock_fast(struct srcu_struct *ssp, struc= t srcu_ctr __percpu *scp) =20 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); =20 -// Record reader usage even for CONFIG_PROVE_RCU=3Dn kernels. This is -// needed only for flavors that require grace-period smp_mb() calls to be -// promoted to synchronize_rcu(). -static inline void srcu_check_read_flavor_force(struct srcu_struct *ssp, i= nt read_flavor) -{ - struct srcu_data *sdp =3D raw_cpu_ptr(ssp->sda); - - if (likely(READ_ONCE(sdp->srcu_reader_flavor) & read_flavor)) - return; - - // Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered. - __srcu_check_read_flavor(ssp, read_flavor); -} - -// Record non-_lite() usage only for CONFIG_PROVE_RCU=3Dy kernels. +// Record SRCU-reader usage type only for CONFIG_PROVE_RCU=3Dy kernels. static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int rea= d_flavor) { if (IS_ENABLED(CONFIG_PROVE_RCU)) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index bf1226834c9423..76f952196a2921 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1600,11 +1600,6 @@ static inline void rcu_tasks_bootup_oddness(void) {} // Tracing variant of Tasks RCU. This variant is designed to be used // to protect tracing hooks, including those of BPF. This variant // is implemented via a straightforward mapping onto SRCU-fast. -// DEFINE_SRCU_FAST() is required because rcu_read_lock_trace() must -// use __srcu_read_lock_fast() in order to bypass the rcu_is_watching() -// checks in kernels built with CONFIG_TASKS_TRACE_RCU_NO_MB=3Dn, which al= so -// bypasses the srcu_check_read_flavor_force() that would otherwise mark -// rcu_tasks_trace_srcu_struct as needing SRCU-fast readers. =20 DEFINE_SRCU_FAST(rcu_tasks_trace_srcu_struct); EXPORT_SYMBOL_GPL(rcu_tasks_trace_srcu_struct); --=20 2.40.1