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=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_IN_DEF_DKIM_WL 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 B7F46C35646 for ; Fri, 21 Feb 2020 17:58:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EBA020722 for ; Fri, 21 Feb 2020 17:58:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Wsv50n8Q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728105AbgBUR6t (ORCPT ); Fri, 21 Feb 2020 12:58:49 -0500 Received: from mail-ot1-f68.google.com ([209.85.210.68]:38841 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725947AbgBUR6t (ORCPT ); Fri, 21 Feb 2020 12:58:49 -0500 Received: by mail-ot1-f68.google.com with SMTP id z9so2785964oth.5 for ; Fri, 21 Feb 2020 09:58:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=02nz5IY2LDSzsi6Uwi52GMpeaKEGb8jSNiWMvCCts+g=; b=Wsv50n8Q9c9FO9EmNBmQOtFrLHiCL1ewuU16RjFVw6klebZY725b8j5BAv8N6Vwj0J sMvP2NGGk5Xh3vofbSSJtcTtIbkOudT1vMKDWYQCEsZ4QvXlNyRidAC5Ok3xyJFzoXeG EM24RX+BP0APhts8JGOywYa5e5T+R0MthuIESWOkGX5zAhQ4v+fGwLtB/iE/wBUN2j2+ QPNY/099g7BpMpx7gs4qnbDrGVLEUlNUAARBq5sfy5dWAzphI/RDEJto7uVqPoyoari7 ZPOKPiCl2CqggebttO9roTZ1S+jV0TpRLl1zSLKiqQKatK9SNrkbBZtcXK58ojXBTcBj gySA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=02nz5IY2LDSzsi6Uwi52GMpeaKEGb8jSNiWMvCCts+g=; b=lhLGHYrJndJiBrZG8xgmR/upcQw2B4JxGFUsXBkNP/nXjs6res9l1h9n07M/r+zQEh pAKhfe4nDQk0SzoTkN3etLSaAgXiy9TpYdi5UWZZ3bjbACi9a0KQmzV/CYjxWtXGBCxt XRtpP3b16yClbQe+DeyN2hBjtSHCs35CE4ZrE9ulw+ePS3QgOgMiHJwHgGWznaodvjFz uUShqrorlzvQMdjRWj/4I00KT/11vRwXmIm2l7vFC09O5z+8Eo8++sRYwfaPMuMSnKZP JS4QVfCvlwNeAWDZh34ixPO+b16Hx5rqGV8ezBVR8pnDzGwWSfZmMiMkBmJGH9KUSGhn Ldqw== X-Gm-Message-State: APjAAAX/DXne9C7pCvDwL4lRyEns6gCorbkWdF8LJoEbNbcHQs4KM689 tPCdyUeNtbkhk1VgE0uWmMG13Z37PEzI3sHzZWyq1w== X-Google-Smtp-Source: APXvYqyTQpLKn5mk9pVf4ftGL846zu9cQ5dx4FwkJ7BtEMT7Fyn5KWCXiAcoZfE44n5b1v+b5nvpdfK5NbPxSBv2pPQ= X-Received: by 2002:a05:6830:1d7b:: with SMTP id l27mr27496908oti.251.1582307927408; Fri, 21 Feb 2020 09:58:47 -0800 (PST) MIME-Version: 1.0 References: <20200219151531.161515-1-elver@google.com> <1582305008.7365.111.camel@lca.pw> In-Reply-To: <1582305008.7365.111.camel@lca.pw> From: Marco Elver Date: Fri, 21 Feb 2020 18:58:36 +0100 Message-ID: Subject: Re: [PATCH] kcsan: Add option for verbose reporting To: Qian Cai Cc: "Paul E. McKenney" , Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , kasan-dev , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 21 Feb 2020 at 18:10, Qian Cai wrote: > > On Wed, 2020-02-19 at 16:15 +0100, Marco Elver wrote: > > Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports. > > Currently information about the reporting task's held locks and IRQ > > trace events are shown, if they are enabled. > > Well, there is a report. I don't understand why it said there is no lock held in > the writer, but clearly there is this right after in > jbd2_journal_commit_transaction(), > > spin_unlock(&jh->b_state_lock); This is sort of expected right now. In the comment that adds this feature, it also has a comment for the "other thread" (in this case the writer): /* * Showing held locks for a running task is unreliable, so just * skip this. The printed locks are very likely inconsistent, * since the stack trace was obtained when the actual race * occurred and the task has since continued execution. Since we * cannot display the below information from the racing thread, * but must print it all from the watcher thread, bail out. * Note: Even if the task is not running, there is a chance that * the locks held may be inconsistent. */ Hmm, I suppose I could try harder and make this reliable by stalling the other task if this option is on. Let me give that a try. Thanks, -- Marco > [ 2268.021382][T25724] BUG: KCSAN: data-race in __jbd2_journal_refile_buffer > [jbd2] / jbd2_write_access_granted [jbd2] > [ 2268.031888][T25724] > [ 2268.034099][T25724] write to 0xffff99f9b1bd0e30 of 8 bytes by task 25721 on > cpu 70: > [ 2268.041842][T25724] __jbd2_journal_refile_buffer+0xdd/0x210 [jbd2] > __jbd2_journal_refile_buffer at fs/jbd2/transaction.c:2569 > [ 2268.048181][T25724] jbd2_journal_commit_transaction+0x2d15/0x3f20 [jbd2] > (inlined by) jbd2_journal_commit_transaction at fs/jbd2/commit.c:1033 > [ 2268.055042][T25724] kjournald2+0x13b/0x450 [jbd2] > [ 2268.059876][T25724] kthread+0x1cd/0x1f0 > [ 2268.063835][T25724] ret_from_fork+0x27/0x50 > [ 2268.068143][T25724] > [ 2268.070348][T25724] no locks held by jbd2/loop0-8/25721. > [ 2268.075699][T25724] irq event stamp: 77604 > [ 2268.079830][T25724] hardirqs last enabled at (77603): [] > _raw_spin_unlock_irqrestore+0x53/0x60 > [ 2268.090166][T25724] hardirqs last disabled at (77604): [] > __schedule+0x181/0xa50 > [ 2268.099192][T25724] softirqs last enabled at (76092): [] > __do_softirq+0x34c/0x57c > [ 2268.108392][T25724] softirqs last disabled at (76005): [] > irq_exit+0xa2/0xc0 > [ 2268.117062][T25724] > [ 2268.119269][T25724] read to 0xffff99f9b1bd0e30 of 8 bytes by task 25724 on > cpu 68: > [ 2268.126916][T25724] jbd2_write_access_granted+0x1b2/0x250 [jbd2] > jbd2_write_access_granted at fs/jbd2/transaction.c:1155 > [ 2268.133086][T25724] jbd2_journal_get_write_access+0x2c/0x60 [jbd2] > [ 2268.139492][T25724] __ext4_journal_get_write_access+0x50/0x90 [ext4] > [ 2268.146076][T25724] ext4_mb_mark_diskspace_used+0x158/0x620 [ext4] > [ 2268.152507][T25724] ext4_mb_new_blocks+0x54f/0xca0 [ext4] > [ 2268.158125][T25724] ext4_ind_map_blocks+0xc79/0x1b40 [ext4] > [ 2268.163923][T25724] ext4_map_blocks+0x3b4/0x950 [ext4] > [ 2268.169284][T25724] _ext4_get_block+0xfc/0x270 [ext4] > [ 2268.174556][T25724] ext4_get_block+0x3b/0x50 [ext4] > [ 2268.179566][T25724] __block_write_begin_int+0x22e/0xae0 > [ 2268.184921][T25724] __block_write_begin+0x39/0x50 > [ 2268.189842][T25724] ext4_write_begin+0x388/0xb50 [ext4] > [ 2268.195195][T25724] generic_perform_write+0x15d/0x290 > [ 2268.200467][T25724] ext4_buffered_write_iter+0x11f/0x210 [ext4] > [ 2268.206612][T25724] ext4_file_write_iter+0xce/0x9e0 [ext4] > [ 2268.212228][T25724] new_sync_write+0x29c/0x3b0 > [ 2268.216794][T25724] __vfs_write+0x92/0xa0 > [ 2268.220924][T25724] vfs_write+0x103/0x260 > [ 2268.225052][T25724] ksys_write+0x9d/0x130 > [ 2268.229182][T25724] __x64_sys_write+0x4c/0x60 > [ 2268.233666][T25724] do_syscall_64+0x91/0xb05 > [ 2268.238058][T25724] entry_SYSCALL_64_after_hwframe+0x49/0xbe > [ 2268.243846][T25724] > [ 2268.246056][T25724] 5 locks held by fsync04/25724: > [ 2268.250880][T25724] #0: ffff99f9911093f8 (sb_writers#13){.+.+}, at: > vfs_write+0x21c/0x260 > [ 2268.259211][T25724] #1: ffff99f9db4c0348 (&sb->s_type- > >i_mutex_key#15){+.+.}, at: ext4_buffered_write_iter+0x65/0x210 [ext4] > [ 2268.270693][T25724] #2: ffff99f5e7dfcf58 (jbd2_handle){++++}, at: > start_this_handle+0x1c1/0x9d0 [jbd2] > [ 2268.280180][T25724] #3: ffff99f9db4c0168 (&ei->i_data_sem){++++}, at: > ext4_map_blocks+0x176/0x950 [ext4] > [ 2268.289913][T25724] #4: ffffffff99086b40 (rcu_read_lock){....}, at: > jbd2_write_access_granted+0x4e/0x250 [jbd2] > [ 2268.300187][T25724] irq event stamp: 1407125 > [ 2268.304496][T25724] hardirqs last enabled at (1407125): [] > __find_get_block+0x107/0x790 > [ 2268.314218][T25724] hardirqs last disabled at (1407124): [] > __find_get_block+0x49/0x790 > [ 2268.323856][T25724] softirqs last enabled at (1405528): [] > __do_softirq+0x34c/0x57c > [ 2268.333229][T25724] softirqs last disabled at (1405521): [] > irq_exit+0xa2/0xc0 > [ 2268.342075][T25724] > [ 2268.344282][T25724] Reported by Kernel Concurrency Sanitizer on: > [ 2268.350339][T25724] CPU: 68 PID: 25724 Comm: fsync04 Tainted: > G L 5.6.0-rc2-next-20200221+ #7 > [ 2268.360234][T25724] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 > Gen10, BIOS A40 07/10/2019 > > > > > Signed-off-by: Marco Elver > > Suggested-by: Qian Cai > > --- > > kernel/kcsan/report.c | 48 +++++++++++++++++++++++++++++++++++++++++++ > > lib/Kconfig.kcsan | 13 ++++++++++++ > > 2 files changed, 61 insertions(+) > > > > diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c > > index 11c791b886f3c..f14becb6f1537 100644 > > --- a/kernel/kcsan/report.c > > +++ b/kernel/kcsan/report.c > > @@ -1,10 +1,12 @@ > > // SPDX-License-Identifier: GPL-2.0 > > > > +#include > > #include > > #include > > #include > > #include > > #include > > +#include > > #include > > #include > > #include > > @@ -245,6 +247,29 @@ static int sym_strcmp(void *addr1, void *addr2) > > return strncmp(buf1, buf2, sizeof(buf1)); > > } > > > > +static void print_verbose_info(struct task_struct *task) > > +{ > > + if (!task) > > + return; > > + > > + if (task != current && task->state == TASK_RUNNING) > > + /* > > + * Showing held locks for a running task is unreliable, so just > > + * skip this. The printed locks are very likely inconsistent, > > + * since the stack trace was obtained when the actual race > > + * occurred and the task has since continued execution. Since we > > + * cannot display the below information from the racing thread, > > + * but must print it all from the watcher thread, bail out. > > + * Note: Even if the task is not running, there is a chance that > > + * the locks held may be inconsistent. > > + */ > > + return; > > + > > + pr_err("\n"); > > + debug_show_held_locks(task); > > + print_irqtrace_events(task); > > +} > > + > > /* > > * Returns true if a report was generated, false otherwise. > > */ > > @@ -319,6 +344,26 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, > > other_info.num_stack_entries - other_skipnr, > > 0); > > > > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE) && other_info.task_pid != -1) { > > + struct task_struct *other_task; > > + > > + /* > > + * Rather than passing @current from the other task via > > + * @other_info, obtain task_struct here. The problem > > + * with passing @current via @other_info is that, we > > + * would have to get_task_struct/put_task_struct, and if > > + * we race with a task being released, we would have to > > + * release it in release_report(). This may result in > > + * deadlock if we want to use KCSAN on the allocators. > > + * Instead, make this best-effort, and if the task was > > + * already released, we just do not print anything here. > > + */ > > + rcu_read_lock(); > > + other_task = find_task_by_pid_ns(other_info.task_pid, &init_pid_ns); > > + print_verbose_info(other_task); > > + rcu_read_unlock(); > > + } > > + > > pr_err("\n"); > > pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", > > get_access_type(access_type), ptr, size, > > @@ -340,6 +385,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, > > stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, > > 0); > > > > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) > > + print_verbose_info(current); > > + > > /* Print report footer. */ > > pr_err("\n"); > > pr_err("Reported by Kernel Concurrency Sanitizer on:\n"); > > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan > > index f0b791143c6ab..ba9268076cfbc 100644 > > --- a/lib/Kconfig.kcsan > > +++ b/lib/Kconfig.kcsan > > @@ -20,6 +20,19 @@ menuconfig KCSAN > > > > if KCSAN > > > > +config KCSAN_VERBOSE > > + bool "Show verbose reports with more information about system state" > > + depends on PROVE_LOCKING > > + help > > + If enabled, reports show more information about the system state that > > + may help better analyze and debug races. This includes held locks and > > + IRQ trace events. > > + > > + While this option should generally be benign, we call into more > > + external functions on report generation; if a race report is > > + generated from any one of them, system stability may suffer due to > > + deadlocks or recursion. If in doubt, say N. > > + > > config KCSAN_DEBUG > > bool "Debugging of KCSAN internals" > >