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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 3DAD8C4360C for ; Thu, 10 Oct 2019 03:08:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0ABA7218DE for ; Thu, 10 Oct 2019 03:08:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570676926; bh=SJDqa0XQ8PdlsODmYo3N8u85qF3dUXq8O5FOKsqgHyc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=MsQDr+V4DBafZ/bBjlDFIR28S467bg9swGymr4mmmCjEI9k+Z7EjgpL3wM1vS5rM+ SS6mA6lsWqsL3sWSJfyngFzgfIFyw5tvhYZ6X03+aTh533ylX9ejnT+RnZSa200vaS puz29LZkNbO98jbli1J5Wf7uDr8j0jBo3TMVDg2A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726465AbfJJDIp (ORCPT ); Wed, 9 Oct 2019 23:08:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:39372 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726478AbfJJDIp (ORCPT ); Wed, 9 Oct 2019 23:08:45 -0400 Received: from paulmck-ThinkPad-P72 (unknown [12.12.162.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9239420650; Thu, 10 Oct 2019 03:08:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570676924; bh=SJDqa0XQ8PdlsODmYo3N8u85qF3dUXq8O5FOKsqgHyc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=0PwYQfX5xZeASc8Kl+Bk0hXaqGBi+ZTFqIdRqJpCNt8+3vxaSG8AnEYtQTPhxjqSs WXUnRYWpsGjosXhc8clJ7bPEq7nkUqhRGtklv4tB1WFDTg0T5seigOgzEZbIxv4Iw3 3MZrXEtPjtE6jQXNsz6GtWi9eoQDVZe6mJovgnpw= Date: Wed, 9 Oct 2019 20:08:39 -0700 From: "Paul E. McKenney" To: Marco Elver Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , Ingo Molnar , Dmitry Vyukov , rcu@vger.kernel.org Subject: Re: [PATCH] rcu: Fix data-race due to atomic_t copy-by-value Message-ID: <20191010030838.GC2689@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191009155743.202142-1-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009155743.202142-1-elver@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Wed, Oct 09, 2019 at 05:57:43PM +0200, Marco Elver wrote: > This fixes a data-race where `atomic_t dynticks` is copied by value. The > copy is performed non-atomically, resulting in a data-race if `dynticks` > is updated concurrently. > > This data-race was found with KCSAN: > ================================================================== > BUG: KCSAN: data-race in dyntick_save_progress_counter / rcu_irq_enter > > write to 0xffff989dbdbe98e0 of 4 bytes by task 10 on cpu 3: > atomic_add_return include/asm-generic/atomic-instrumented.h:78 [inline] > rcu_dynticks_snap kernel/rcu/tree.c:310 [inline] > dyntick_save_progress_counter+0x43/0x1b0 kernel/rcu/tree.c:984 > force_qs_rnp+0x183/0x200 kernel/rcu/tree.c:2286 > rcu_gp_fqs kernel/rcu/tree.c:1601 [inline] > rcu_gp_fqs_loop+0x71/0x880 kernel/rcu/tree.c:1653 > rcu_gp_kthread+0x22c/0x3b0 kernel/rcu/tree.c:1799 > kthread+0x1b5/0x200 kernel/kthread.c:255 > > > read to 0xffff989dbdbe98e0 of 4 bytes by task 154 on cpu 7: > rcu_nmi_enter_common kernel/rcu/tree.c:828 [inline] > rcu_irq_enter+0xda/0x240 kernel/rcu/tree.c:870 > irq_enter+0x5/0x50 kernel/softirq.c:347 > > > Reported by Kernel Concurrency Sanitizer on: > CPU: 7 PID: 154 Comm: kworker/7:1H Not tainted 5.3.0+ #5 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > Workqueue: kblockd blk_mq_run_work_fn > ================================================================== > > Signed-off-by: Marco Elver Good catch, queued for review and testing. Thanx, Paul > Cc: Paul E. McKenney > Cc: Josh Triplett > Cc: Steven Rostedt > Cc: Mathieu Desnoyers > Cc: Lai Jiangshan > Cc: Joel Fernandes > Cc: Ingo Molnar > Cc: Dmitry Vyukov > Cc: rcu@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > --- > include/trace/events/rcu.h | 4 ++-- > kernel/rcu/tree.c | 11 ++++++----- > 2 files changed, 8 insertions(+), 7 deletions(-) > > diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h > index 694bd040cf51..fdd31c5fd126 100644 > --- a/include/trace/events/rcu.h > +++ b/include/trace/events/rcu.h > @@ -442,7 +442,7 @@ TRACE_EVENT_RCU(rcu_fqs, > */ > TRACE_EVENT_RCU(rcu_dyntick, > > - TP_PROTO(const char *polarity, long oldnesting, long newnesting, atomic_t dynticks), > + TP_PROTO(const char *polarity, long oldnesting, long newnesting, int dynticks), > > TP_ARGS(polarity, oldnesting, newnesting, dynticks), > > @@ -457,7 +457,7 @@ TRACE_EVENT_RCU(rcu_dyntick, > __entry->polarity = polarity; > __entry->oldnesting = oldnesting; > __entry->newnesting = newnesting; > - __entry->dynticks = atomic_read(&dynticks); > + __entry->dynticks = dynticks; > ), > > TP_printk("%s %lx %lx %#3x", __entry->polarity, > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 81105141b6a8..62e59596a30a 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -576,7 +576,7 @@ static void rcu_eqs_enter(bool user) > } > > lockdep_assert_irqs_disabled(); > - trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks); > + trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks)); > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); > rdp = this_cpu_ptr(&rcu_data); > do_nocb_deferred_wakeup(rdp); > @@ -649,14 +649,15 @@ static __always_inline void rcu_nmi_exit_common(bool irq) > * leave it in non-RCU-idle state. > */ > if (rdp->dynticks_nmi_nesting != 1) { > - trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks); > + 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. */ > rdp->dynticks_nmi_nesting - 2); > return; > } > > /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ > - trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, rdp->dynticks); > + 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 (irq) > @@ -743,7 +744,7 @@ static void rcu_eqs_exit(bool user) > rcu_dynticks_task_exit(); > rcu_dynticks_eqs_exit(); > rcu_cleanup_after_idle(); > - trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks); > + 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)); > WRITE_ONCE(rdp->dynticks_nesting, 1); > WARN_ON_ONCE(rdp->dynticks_nmi_nesting); > @@ -827,7 +828,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq) > } > trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), > rdp->dynticks_nmi_nesting, > - rdp->dynticks_nmi_nesting + incby, rdp->dynticks); > + rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks)); > WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */ > rdp->dynticks_nmi_nesting + incby); > barrier(); > -- > 2.23.0.581.g78d2f28ef7-goog >