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=-20.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 7613DC6377A for ; Wed, 21 Jul 2021 20:38:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5E62961246 for ; Wed, 21 Jul 2021 20:38:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233136AbhGUT5u (ORCPT ); Wed, 21 Jul 2021 15:57:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:56324 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231344AbhGUT5p (ORCPT ); Wed, 21 Jul 2021 15:57:45 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8DB8A61222; Wed, 21 Jul 2021 20:38:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1626899901; bh=oKLPW9M7jcs30XzmVmiWriCs3Z6UUgtAL+H/Eg8hXHw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=R60aWChv4EEBRGiUmWFcSTDQlTJAvcDqblg5wLQk+Yh4GAORoLG0I7WaPsuuFFbrm 9h4jcyu0+nb4B2/z+LUSekzGIXv1EO8N5qG77co8Fwx5zdPv7hBADEFkXsGytYjAux yj+VoW2EY6d/lnjpi/z4XoVNVSrawXfDpL7OL38HsYsdqfS3hUcKRjyWVphHHbImq9 l/AnydfmLKlAM6hasNyHR3ohSLgecZgiMU9as5seDbumyZ3KATy0wYDVkH4PfOfv/y vuVVrKTKJRPS4Ij/s32Y2VVWXhi2Eub4inym3SVlRaRU51c84EU+NDDvGOF918n3OY LypBPwWiGLjHQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 550E55C0A03; Wed, 21 Jul 2021 13:38:21 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH rcu 2/5] rcu-tasks: Mark ->trc_reader_nesting data races Date: Wed, 21 Jul 2021 13:38:15 -0700 Message-Id: <20210721203818.3398345-2-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20210721203758.GA3386731@paulmck-ThinkPad-P17-Gen-1> References: <20210721203758.GA3386731@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There are several ->trc_reader_nesting data races that are too low-probability for KCSAN to notice, but which will happen sooner or later. This commit therefore marks these accesses, and comments one that cannot race. Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 6a117375a62a1..f6b5320c44849 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -897,7 +897,7 @@ static void trc_read_check_handler(void *t_in) // If the task is not in a read-side critical section, and // if this is the last reader, awaken the grace-period kthread. - if (likely(!t->trc_reader_nesting)) { + if (likely(!READ_ONCE(t->trc_reader_nesting))) { if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) wake_up(&trc_wait); // Mark as checked after decrement to avoid false @@ -906,7 +906,7 @@ static void trc_read_check_handler(void *t_in) goto reset_ipi; } // If we are racing with an rcu_read_unlock_trace(), try again later. - if (unlikely(t->trc_reader_nesting < 0)) { + if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0)) { if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) wake_up(&trc_wait); goto reset_ipi; @@ -953,6 +953,7 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg) n_heavy_reader_ofl_updates++; in_qs = true; } else { + // The task is not running, so C-language access is safe. in_qs = likely(!t->trc_reader_nesting); } @@ -985,7 +986,7 @@ static void trc_wait_for_one_reader(struct task_struct *t, // The current task had better be in a quiescent state. if (t == current) { t->trc_reader_checked = true; - WARN_ON_ONCE(t->trc_reader_nesting); + WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); return; } @@ -1101,7 +1102,7 @@ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0], ".i"[is_idle_task(t)], ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)], - t->trc_reader_nesting, + READ_ONCE(t->trc_reader_nesting), " N"[!!t->trc_reader_special.b.need_qs], cpu); sched_show_task(t); @@ -1196,7 +1197,7 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) static void exit_tasks_rcu_finish_trace(struct task_struct *t) { WRITE_ONCE(t->trc_reader_checked, true); - WARN_ON_ONCE(t->trc_reader_nesting); + WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); WRITE_ONCE(t->trc_reader_nesting, 0); if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs))) rcu_read_unlock_trace_special(t, 0); -- 2.31.1.189.g2e36527f23