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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 87266CA9ED3 for ; Mon, 4 Nov 2019 16:53:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 513232080F for ; Mon, 4 Nov 2019 16:53:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572886388; bh=3v2OwxHCxuhPKIdIGxXQQCJnZq6WAgU4/prpwyx4VwU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=hVX0XrQbujNQAnb1JjLJlWxZomE01BwkO6AXcgAHy89ZXJthWCs5y82N8zBYcHarH QMD8NzT9+ymNenXNBqh3JisvcBA1wfzE9e2VNpLaFVRAbSaUj9D+SzetyDJlX4YrJg JFx8bmR1ZO0VTyP4aoYnMneaAkN5YkbMaAan3Rs4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729341AbfKDQxH (ORCPT ); Mon, 4 Nov 2019 11:53:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:40190 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728705AbfKDQxH (ORCPT ); Mon, 4 Nov 2019 11:53:07 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [109.144.216.141]) (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 0898E2080F; Mon, 4 Nov 2019 16:53:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572886385; bh=3v2OwxHCxuhPKIdIGxXQQCJnZq6WAgU4/prpwyx4VwU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=bzUs+po8ejq0GRqnkWvP44HRLEyigCVv8BOA03jBD4hXxOVoIkIBGhfOrdrUPjBEQ 1uM149r+fdiRqkND8KQaHOjDstfijFmzIYJsUoRJwJABjR/eN2EpWNBxxYowptiCxN 1+TfwRrpU3/9P6x3j+4tJ6FcAKiSUPCCQh7XMZt4= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 282243520B56; Mon, 4 Nov 2019 08:53:03 -0800 (PST) Date: Mon, 4 Nov 2019 08:53:03 -0800 From: "Paul E. McKenney" To: Marco Elver Cc: syzbot , Lai Jiangshan , Josh Triplett , axboe@kernel.dk, justin@coraid.com, linux-block@vger.kernel.org, LKML , syzkaller-bugs@googlegroups.com Subject: Re: KCSAN: data-race in process_srcu / synchronize_srcu Message-ID: <20191104165303.GG20975@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <000000000000b587670596839fab@google.com> <20191104161152.GB20975@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 04, 2019 at 05:14:50PM +0100, Marco Elver wrote: > On Mon, 4 Nov 2019 at 17:11, Paul E. McKenney wrote: > > > > On Mon, Nov 04, 2019 at 12:31:56PM +0100, Marco Elver wrote: > > > +RCU folks, since this is probably a data race in RCU. > > > > > > On Mon, 4 Nov 2019 at 12:29, syzbot > > > wrote: > > > > > > > > Hello, > > > > > > > > syzbot found the following crash on: > > > > > > > > HEAD commit: 05f22368 x86, kcsan: Enable KCSAN for x86 > > > > git tree: https://github.com/google/ktsan.git kcsan > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17ade7ef600000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=08f3e9d26e5541e1ecf2 > > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > > > > > Unfortunately, I don't have any reproducer for this crash yet. > > > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > > Reported-by: syzbot+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com > > > > > > > > ================================================================== > > > > BUG: KCSAN: data-race in process_srcu / synchronize_srcu > > > > > > > > write to 0xffffffff8604e8a0 of 8 bytes by task 17 on cpu 1: > > > > srcu_gp_end kernel/rcu/srcutree.c:533 [inline] > > > > srcu_advance_state kernel/rcu/srcutree.c:1146 [inline] > > > > process_srcu+0x207/0x780 kernel/rcu/srcutree.c:1237 > > > > process_one_work+0x3d4/0x890 kernel/workqueue.c:2269 > > > > worker_thread+0xa0/0x800 kernel/workqueue.c:2415 > > > > kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 > > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 > > > > > > > > read to 0xffffffff8604e8a0 of 8 bytes by task 12515 on cpu 0: > > > > srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline] > > > > synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996 > > > > fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164 > > > > process_one_work+0x3d4/0x890 kernel/workqueue.c:2269 > > > > worker_thread+0xa0/0x800 kernel/workqueue.c:2415 > > > > kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 > > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 > > > > > > > > Reported by Kernel Concurrency Sanitizer on: > > > > CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0 > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > > > Google 01/01/2011 > > > > Workqueue: events_unbound fsnotify_connector_destroy_workfn > > > > ================================================================== > > > > Kernel panic - not syncing: panic_on_warn set ... > > > > CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0 > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > > > Google 01/01/2011 > > > > Workqueue: events_unbound fsnotify_connector_destroy_workfn > > > > Call Trace: > > > > __dump_stack lib/dump_stack.c:77 [inline] > > > > dump_stack+0xf5/0x159 lib/dump_stack.c:113 > > > > panic+0x210/0x640 kernel/panic.c:221 > > > > kcsan_report.cold+0xc/0x10 kernel/kcsan/report.c:302 > > > > __kcsan_setup_watchpoint+0x32e/0x4a0 kernel/kcsan/core.c:411 > > > > __tsan_read8 kernel/kcsan/kcsan.c:36 [inline] > > > > __tsan_read8+0x2c/0x30 kernel/kcsan/kcsan.c:36 > > > > srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline] > > > > synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996 > > > > fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164 > > > > process_one_work+0x3d4/0x890 kernel/workqueue.c:2269 > > > > worker_thread+0xa0/0x800 kernel/workqueue.c:2415 > > > > kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 > > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 > > > > Kernel Offset: disabled > > > > Rebooting in 86400 seconds.. > > > > > > > > > > > > --- > > > > This bug is generated by a bot. It may contain errors. > > > > See https://goo.gl/tpsmEJ for more information about syzbot. > > > > syzbot engineers can be reached at syzkaller@googlegroups.com. > > > > > > > > syzbot will keep track of this bug report. See: > > > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > > > Good catch! Does the patch below help? > > Looks good to me, thanks for the quick fix. > > Acked-by: Marco Elver Applied, thank you! Thanx, Paul > Thanks, > -- Marco > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit d2ab457602a59353b8853352735dfd094d223480 > > Author: Paul E. McKenney > > Date: Mon Nov 4 08:08:30 2019 -0800 > > > > srcu: Apply *_ONCE() to ->srcu_last_gp_end > > > > The ->srcu_last_gp_end field is accessed from any CPU at any time > > by synchronize_srcu(), so non-initialization references need to use > > READ_ONCE() and WRITE_ONCE(). This commit therefore makes that change. > > > > Reported-by: syzbot+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com > > Signed-off-by: Paul E. McKenney > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index d0a9d5b..657e6a7 100644 > > --- a/kernel/rcu/srcutree.c > > +++ b/kernel/rcu/srcutree.c > > @@ -530,7 +530,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) > > idx = rcu_seq_state(ssp->srcu_gp_seq); > > WARN_ON_ONCE(idx != SRCU_STATE_SCAN2); > > cbdelay = srcu_get_delay(ssp); > > - ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); > > + WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns()); > > rcu_seq_end(&ssp->srcu_gp_seq); > > gpseq = rcu_seq_current(&ssp->srcu_gp_seq); > > if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq)) > > @@ -762,6 +762,7 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) > > unsigned long flags; > > struct srcu_data *sdp; > > unsigned long t; > > + unsigned long tlast; > > > > /* If the local srcu_data structure has callbacks, not idle. */ > > local_irq_save(flags); > > @@ -780,9 +781,9 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) > > > > /* First, see if enough time has passed since the last GP. */ > > t = ktime_get_mono_fast_ns(); > > + tlast = READ_ONCE(ssp->srcu_last_gp_end); > > if (exp_holdoff == 0 || > > - time_in_range_open(t, ssp->srcu_last_gp_end, > > - ssp->srcu_last_gp_end + exp_holdoff)) > > + time_in_range_open(t, tlast, tlast + exp_holdoff)) > > return false; /* Too soon after last GP. */ > > > > /* Next, check for probable idleness. */