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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19D93C433EF for ; Tue, 19 Apr 2022 00:03:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237398AbiDSAGg (ORCPT ); Mon, 18 Apr 2022 20:06:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52780 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236855AbiDSAGJ (ORCPT ); Mon, 18 Apr 2022 20:06:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B0572317E; Mon, 18 Apr 2022 17:03:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 20FB1612D0; Tue, 19 Apr 2022 00:03:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13CF9C385BA; Tue, 19 Apr 2022 00:03:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650326605; bh=yD8/2f4i74rv4I75fc7QN5JRO3/GVs7/E4TdpFpPISc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=R8q1Cv0Vkp9q/MSz5wqfJReVoVMUwgvmUz05/uY8RS055LvWx/W+JI1bSz3Is/ZF3 IUxNeKNZ+Mhn0pvn4N3ww4zCDyaRswoa5ikzO8JKIMYKKnssJEVK62xfx9Fz8zvuoz 9Tdzzv4U7sIanHJZPGP83cSVCq9WSvhhTR0b+s9M9FTWDjwG1drc51ncTX8wh794Ho 3HKIUl5pjft6Iltsrdko7douITCeRHpiscJ3Clug/FV35HF0ga/bnFWXx0JbpqlAdq lz4PGDv0xOOXhLNxtxrb6bsJlAHxUGp+C0mHhAP7yyvFYLtnhzYZUnlvn2PWsjxq6o DHcOvA7ZRgF4Q== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 644845C23F4; Mon, 18 Apr 2022 17:03:24 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, "Paul E. McKenney" , Neeraj Upadhyay Subject: [PATCH rcu 13/21] srcu: Avoid NULL dereference in srcu_torture_stats_print() Date: Mon, 18 Apr 2022 17:03:14 -0700 Message-Id: <20220419000322.3948903-13-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220419000315.GA3948789@paulmck-ThinkPad-P17-Gen-1> References: <20220419000315.GA3948789@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 You really shouldn't invoke srcu_torture_stats_print() after invoking cleanup_srcu_struct(), but there is really no reason to get a compiler-obfuscated per-CPU-variable NULL pointer dereference as the diagnostic. This commit therefore checks for NULL ->sda and makes a more polite console-message complaint in that case. Co-developed-by: Neeraj Upadhyay Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 62 ++++++++++++++++++++++++------------------- 1 file changed, 34 insertions(+), 28 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 9dd048989027..b7138dbe1a2d 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1477,37 +1477,43 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) idx = ssp->srcu_idx & 0x1; if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name)) ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1; - pr_alert("%s%s Tree SRCU g%ld state %d (%s) per-CPU(idx=%d):", + pr_alert("%s%s Tree SRCU g%ld state %d (%s)", tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), ss_state, - srcu_size_state_name[ss_state_idx], idx); - for_each_possible_cpu(cpu) { - unsigned long l0, l1; - unsigned long u0, u1; - long c0, c1; - struct srcu_data *sdp; - - sdp = per_cpu_ptr(ssp->sda, cpu); - u0 = data_race(sdp->srcu_unlock_count[!idx]); - u1 = data_race(sdp->srcu_unlock_count[idx]); + srcu_size_state_name[ss_state_idx]); + if (!ssp->sda) { + // Called after cleanup_srcu_struct(), perhaps. + pr_cont(" No per-CPU srcu_data structures (->sda == NULL).\n"); + } else { + pr_cont(" per-CPU(idx=%d):", idx); + for_each_possible_cpu(cpu) { + unsigned long l0, l1; + unsigned long u0, u1; + long c0, c1; + struct srcu_data *sdp; - /* - * Make sure that a lock is always counted if the corresponding - * unlock is counted. - */ - smp_rmb(); - - l0 = data_race(sdp->srcu_lock_count[!idx]); - l1 = data_race(sdp->srcu_lock_count[idx]); - - c0 = l0 - u0; - c1 = l1 - u1; - pr_cont(" %d(%ld,%ld %c)", - cpu, c0, c1, - "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]); - s0 += c0; - s1 += c1; + sdp = per_cpu_ptr(ssp->sda, cpu); + u0 = data_race(sdp->srcu_unlock_count[!idx]); + u1 = data_race(sdp->srcu_unlock_count[idx]); + + /* + * Make sure that a lock is always counted if the corresponding + * unlock is counted. + */ + smp_rmb(); + + l0 = data_race(sdp->srcu_lock_count[!idx]); + l1 = data_race(sdp->srcu_lock_count[idx]); + + c0 = l0 - u0; + c1 = l1 - u1; + pr_cont(" %d(%ld,%ld %c)", + cpu, c0, c1, + "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]); + s0 += c0; + s1 += c1; + } + pr_cont(" T(%ld,%ld)\n", s0, s1); } - pr_cont(" T(%ld,%ld)\n", s0, s1); if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 2) WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_ALLOC); } -- 2.31.1.189.g2e36527f23