From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B095C433E0 for ; Mon, 15 Jun 2020 16:24:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2FC3D2078E for ; Mon, 15 Jun 2020 16:24:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kVqXru94" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731163AbgFOQYh (ORCPT ); Mon, 15 Jun 2020 12:24:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55870 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731154AbgFOQYg (ORCPT ); Mon, 15 Jun 2020 12:24:36 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14BC5C061A0E for ; Mon, 15 Jun 2020 09:24:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=UJfkIp8eAX3oRf38KIcxAmyB5E1JmZKm235O+JB/jIk=; b=kVqXru94VUVkOwInbNsGARN7J/ /rs9mTMp5j1tMw7lg/jrpXEX96pF2704hlx0fIk3w+E/qVPVVb8sKzXJwxKz5eyaYEouEzYlpkW1N 8LbLgVHqWi8PM/EZBH2jUnS/DzqdbSnaatAH6Eu6ui2qfUegQZ2LbpsDC066wjEAfpyt3Jrjrp/Fy iQzlgsvf/8rdPKvokUayKypJrPldm8zW5jSn2vCQcSI8uYyxN/F0vzE3MihFp7TM5mFKE+LuX7LgT WxCFkzZmIMRY+WuuWg4bNaNTd9s/Nt+XCjiymy2PPS8dtipfytyHl+E1AQJktBzrzL2FtYZ43D5x1 gsfIeADg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jkruP-0005t4-9S; Mon, 15 Jun 2020 16:24:29 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4F96230753E; Mon, 15 Jun 2020 18:24:27 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 36565203C3762; Mon, 15 Jun 2020 18:24:27 +0200 (CEST) Date: Mon, 15 Jun 2020 18:24:27 +0200 From: Peter Zijlstra To: tglx@linutronix.de Cc: x86@kernel.org, elver@google.com, paulmck@kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, will@kernel.org, dvyukov@google.com, glider@google.com, andreyknvl@google.com Subject: Re: [PATCH 2/9] rcu: Fixup noinstr warnings Message-ID: <20200615162427.GI2554@hirez.programming.kicks-ass.net> References: <20200603114014.152292216@infradead.org> <20200603114051.896465666@infradead.org> <20200615154905.GZ2531@hirez.programming.kicks-ass.net> <20200615155513.GG2554@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200615155513.GG2554@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 15, 2020 at 05:55:13PM +0200, Peter Zijlstra wrote: > On Mon, Jun 15, 2020 at 05:49:05PM +0200, Peter Zijlstra wrote: > > @@ -983,13 +993,17 @@ noinstr void rcu_nmi_enter(void) > > if (!in_nmi()) > > rcu_cleanup_after_idle(); > > > > + instrumentation_begin(); > > + // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs() > > + instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks)); > > + // instrumentation for the noinstr rcu_dynticks_eqs_exit() > > + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); > > + > > incby = 1; > > } else if (!in_nmi()) { > > instrumentation_begin(); > > rcu_irq_enter_check_tick(); > > - instrumentation_end(); > > } > > - instrumentation_begin(); > > trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), > > rdp->dynticks_nmi_nesting, > > rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks)); > > Oh, that's lost a possible instrumentation_begin() :/ But weirdly > objtool didn't complain about that... Let me poke at that. Like so then... --- Subject: rcu: Fixup noinstr warnings A KCSAN build revealed we have explicit annoations through atomic_*() usage, switch to arch_atomic_*() for the respective functions. vmlinux.o: warning: objtool: rcu_nmi_exit()+0x4d: call to __kcsan_check_access() leaves .noinstr.text section vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x25: call to __kcsan_check_access() leaves .noinstr.text section vmlinux.o: warning: objtool: rcu_nmi_enter()+0x4f: call to __kcsan_check_access() leaves .noinstr.text section vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x2a: call to __kcsan_check_access() leaves .noinstr.text section vmlinux.o: warning: objtool: __rcu_is_watching()+0x25: call to __kcsan_check_access() leaves .noinstr.text section Additionally, without the NOP in instrumentation_begin(), objtool would not detect the lack of the 'else instrumentation_begin();' branch in rcu_nmi_enter(). Signed-off-by: Peter Zijlstra (Intel) --- include/linux/compiler.h | 2 +- kernel/rcu/tree.c | 33 +++++++++++++++++++++++++-------- 2 files changed, 26 insertions(+), 9 deletions(-) --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -123,7 +123,7 @@ void ftrace_likely_update(struct ftrace_ #ifdef CONFIG_DEBUG_ENTRY /* Begin/end of an instrumentation safe region */ #define instrumentation_begin() ({ \ - asm volatile("%c0:\n\t" \ + asm volatile("%c0: nop\n\t" \ ".pushsection .discard.instr_begin\n\t" \ ".long %c0b - .\n\t" \ ".popsection\n\t" : : "i" (__COUNTER__)); \ --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -250,7 +250,7 @@ static noinstr void rcu_dynticks_eqs_ent * next idle sojourn. */ rcu_dynticks_task_trace_enter(); // Before ->dynticks update! - seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); + seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); // RCU is no longer watching. Better be in extended quiescent state! WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & RCU_DYNTICK_CTRL_CTR)); @@ -274,13 +274,13 @@ static noinstr void rcu_dynticks_eqs_exi * and we also must force ordering with the next RCU read-side * critical section. */ - seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); + seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); // RCU is now watching. Better not be in an extended quiescent state! rcu_dynticks_task_trace_exit(); // After ->dynticks update! WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & RCU_DYNTICK_CTRL_CTR)); if (seq & RCU_DYNTICK_CTRL_MASK) { - atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks); + arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks); smp_mb__after_atomic(); /* _exit after clearing mask. */ } } @@ -313,7 +313,7 @@ static __always_inline bool rcu_dynticks { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR); + return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR); } /* @@ -633,6 +633,10 @@ static noinstr void rcu_eqs_enter(bool u do_nocb_deferred_wakeup(rdp); rcu_prepare_for_idle(); rcu_preempt_deferred_qs(current); + + // instrumentation for the noinstr rcu_dynticks_eqs_enter() + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); + instrumentation_end(); WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */ // RCU is watching here ... @@ -692,6 +696,7 @@ noinstr void rcu_nmi_exit(void) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + instrumentation_begin(); /* * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. * (We are exiting an NMI handler, so RCU better be paying attention @@ -705,7 +710,6 @@ noinstr void rcu_nmi_exit(void) * leave it in non-RCU-idle state. */ if (rdp->dynticks_nmi_nesting != 1) { - instrumentation_begin(); trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, atomic_read(&rdp->dynticks)); WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */ @@ -714,13 +718,15 @@ noinstr void rcu_nmi_exit(void) return; } - instrumentation_begin(); /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks)); WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ if (!in_nmi()) rcu_prepare_for_idle(); + + // instrumentation for the noinstr rcu_dynticks_eqs_enter() + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); instrumentation_end(); // RCU is watching here ... @@ -838,6 +844,10 @@ static void noinstr rcu_eqs_exit(bool us rcu_dynticks_eqs_exit(); // ... but is watching here. instrumentation_begin(); + + // instrumentation for the noinstr rcu_dynticks_eqs_exit() + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); + rcu_cleanup_after_idle(); trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks)); WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); @@ -983,13 +993,20 @@ noinstr void rcu_nmi_enter(void) if (!in_nmi()) rcu_cleanup_after_idle(); + instrumentation_begin(); + // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs() + instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks)); + // instrumentation for the noinstr rcu_dynticks_eqs_exit() + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); + incby = 1; } else if (!in_nmi()) { instrumentation_begin(); rcu_irq_enter_check_tick(); - instrumentation_end(); + } else { + instrumentation_begin(); } - instrumentation_begin(); + trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));