From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DB62548035C; Wed, 29 Jul 2026 16:23:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785342184; cv=none; b=do3mMLqCFRCk9e8vNgm97sNzC41mUQY5kbC5VldPQM/mDWakJK+TGvAtHVm77RRl6MXEJfKFkmCPT/drCo9eoim4zSP++nR29wayYnTkOwknyGjPIp1DOW6WIL6rQM5EIEBQk24iC6BwJmfXQOkTH96WDWpoiCfCGKHAGh8b7WI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785342184; c=relaxed/simple; bh=NM20lGHadHSn6VMe6w4FA0M08cTzh4u0xz16qzUTfRw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XGoaRtvFow501CDkxHLy4UvBeU8peMV2vQZmFAI35tqZCDuaCFiyA3lRUrO4PhEok8VJkfLugFXk7nbED0/Lzp+vIZuLKKmYmcr6xNIwlDPyxkz3aSf5VjkJii8GZg13hiXEIc/M7/7sDkwC5D9jOw/itSYjE4B6t32W1sGpetw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BMzatcf3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BMzatcf3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88D0B1F000E9; Wed, 29 Jul 2026 16:23:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785342182; bh=Omh6hJitRM4yP0f4x9s7hhDvDCVb3NchUBaIxLXUGkM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BMzatcf3GGO2FLRWx+un4FtC9470r/dollqI5nx8AmO/ol3nJ972v7yj8WcG+6ste CueT30BY+R928uAkjFZ6RVe69YdBSZOs8mxyc7R28lrXlSygmCnY1oHfQwxuQg7dah 250RDmINglgVjkWmYDXSZCsYQRYaIzrhJDfY2DQyPPPH+L69yg/cw43lUCToSG87Xz oj/s1fEEUS/oZ3m0oc+RlYevzyjqudZviAk4Q9s8oohr/jB32cDrbPBpcXx2S+lNU0 F828DJwPMBcumM17uPofjq3AiRlILktFBdbd/E6YKA/F5z0t8URSzt4e95oxp/NRwZ TOg6RwnPCtzAw== From: Puranjay Mohan To: Lai Jiangshan , "Paul E. McKenney" , Josh Triplett , =?UTF-8?q?Onur=20=C3=96zkan?= , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Uladzislau Rezki , Davidlohr Bueso , Andrii Nakryiko , Eduard Zingerman , Alexei Starovoitov , Daniel Borkmann , Kumar Kartikeya Dwivedi Cc: Puranjay Mohan , Steven Rostedt , Mathieu Desnoyers , Zqiang , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Matt Fleming , "Harry Yoo (Oracle)" , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, bpf@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: [PATCH 4/6] srcu: Make Tiny call_srcu() safe to call from any context Date: Wed, 29 Jul 2026 09:22:03 -0700 Message-ID: <20260729162207.1567770-5-puranjay@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260729162207.1567770-1-puranjay@kernel.org> References: <20260729162207.1567770-1-puranjay@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Make Tiny call_srcu() safe to call from unknown context: when interrupts are disabled and the scheduler is up, stage the callback on the srcu_struct's lockless list that an irq_work re-issues later. Tiny SRCU is uniprocessor, so there is no CPU-offline drain. Gated by CONFIG_RCU_DEFER, like Tree SRCU. Suggested-by: Paul E. McKenney Signed-off-by: Puranjay Mohan --- include/linux/srcutiny.h | 11 ++++++--- kernel/rcu/srcutiny.c | 53 +++++++++++++++++++++++++++++++++++++--- 2 files changed, 56 insertions(+), 8 deletions(-) diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index fbcf13bc12d15..47275d182966c 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -12,6 +12,7 @@ #define _LINUX_SRCU_TINY_H #include +#include #include struct srcu_struct { @@ -26,6 +27,8 @@ struct srcu_struct { struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */ struct work_struct srcu_work; /* For driving grace periods. */ struct irq_work srcu_irq_work; /* Defer schedule_work() to irq work. */ + struct llist_head defer_cbs; /* Callbacks deferred on re-entry. */ + struct irq_work defer_iw; /* Registers defer_cbs later. */ #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ @@ -33,6 +36,7 @@ struct srcu_struct { void srcu_drive_gp(struct work_struct *wp); void srcu_tiny_irq_work(struct irq_work *irq_work); +void srcu_defer_drain(struct irq_work *irq_work); #define __SRCU_STRUCT_INIT(name, __ignored, ___ignored, ____ignored) \ { \ @@ -40,6 +44,8 @@ void srcu_tiny_irq_work(struct irq_work *irq_work); .srcu_cb_tail = &name.srcu_cb_head, \ .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \ .srcu_irq_work = { .func = srcu_tiny_irq_work }, \ + .defer_cbs = LLIST_HEAD_INIT(name.defer_cbs), \ + .defer_iw = { .func = srcu_defer_drain }, \ __SRCU_DEP_MAP_INIT(name) \ } @@ -131,10 +137,7 @@ static inline void synchronize_srcu_expedited(struct srcu_struct *ssp) synchronize_srcu(ssp); } -static inline void srcu_barrier(struct srcu_struct *ssp) -{ - synchronize_srcu(ssp); -} +void srcu_barrier(struct srcu_struct *ssp); static inline void srcu_expedite_current(struct srcu_struct *ssp) { } #define srcu_check_read_flavor(ssp, read_flavor) do { } while (0) diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index f9c498ae75df2..b454d3e828edc 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -10,6 +10,7 @@ #include #include +#include #include #include #include @@ -43,6 +44,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp) INIT_WORK(&ssp->srcu_work, srcu_drive_gp); INIT_LIST_HEAD(&ssp->srcu_work.entry); init_irq_work(&ssp->srcu_irq_work, srcu_tiny_irq_work); + init_llist_head(&ssp->defer_cbs); + init_irq_work(&ssp->defer_iw, srcu_defer_drain); return 0; } @@ -215,11 +218,11 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp) } /* - * Enqueue an SRCU callback on the specified srcu_struct structure, - * initiating grace-period processing if it is not already running. + * Enqueue @rhp on the callback list. Also called by srcu_defer_drain() to + * re-issue a deferred callback, so it must not re-check the deferral condition. */ -void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, - rcu_callback_t func) +static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp, + rcu_callback_t func) { unsigned long flags; @@ -233,6 +236,39 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, srcu_gp_start_if_needed(ssp); preempt_enable(); } + +void srcu_defer_drain(struct irq_work *iw) +{ + struct srcu_struct *ssp = container_of(iw, struct srcu_struct, defer_iw); + struct llist_node *node, *next; + + /* + * Callbacks have no mutual ordering guarantee and srcu_barrier() has + * already flushed us, so drain in llist order without reversing. + */ + llist_for_each_safe(node, next, llist_del_all(&ssp->defer_cbs)) { + struct rcu_head *rhp = (struct rcu_head *)node; + + srcu_do_enqueue(ssp, rhp, rhp->func); + } +} +EXPORT_SYMBOL_GPL(srcu_defer_drain); + +void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, + rcu_callback_t func) +{ + if (should_rcu_defer()) { + rhp->func = func; + if (llist_add((struct llist_node *)rhp, &ssp->defer_cbs)) + irq_work_queue(&ssp->defer_iw); + return; + } + + /* An NMI reaching here entered with irqs enabled, so the enqueue can race. */ + WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi()); + + srcu_do_enqueue(ssp, rhp, func); +} EXPORT_SYMBOL_GPL(call_srcu); /* @@ -262,6 +298,15 @@ void synchronize_srcu(struct srcu_struct *ssp) } EXPORT_SYMBOL_GPL(synchronize_srcu); +/* Register any deferred callbacks, then wait for all in-flight ones. */ +void srcu_barrier(struct srcu_struct *ssp) +{ + if (IS_ENABLED(CONFIG_RCU_DEFER)) + irq_work_sync(&ssp->defer_iw); + synchronize_srcu(ssp); +} +EXPORT_SYMBOL_GPL(srcu_barrier); + /* * get_state_synchronize_srcu - Provide an end-of-grace-period cookie */ -- 2.53.0-Meta