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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 CC1E9CA9ED3 for ; Mon, 4 Nov 2019 22:01:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A05EA20650 for ; Mon, 4 Nov 2019 22:01:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572904917; bh=pTNpI8krUYYgmHKAFknIIvE6NqLq8p5eAggBhfZj+Vw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=tmTplY3AdPTtb9tHPMd0QXuG79wXsae26JPi9iHlaN9fA+Fc96xaNKj+L4QeENXBu +wKbDORGp5/ZcV0japto0U5SS/nUZ3cnM87Wq2LG2C7K2bMCojNw7LXfrnyHtMrae3 KkwjqLX//CaOze0qt9B4NC/vaIbgCJwyiSKiDWb4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389103AbfKDWBz (ORCPT ); Mon, 4 Nov 2019 17:01:55 -0500 Received: from mail.kernel.org ([198.145.29.99]:59308 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388997AbfKDWBP (ORCPT ); Mon, 4 Nov 2019 17:01:15 -0500 Received: from localhost (6.204-14-84.ripe.coltfrance.com [84.14.204.6]) (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 B4CF72084D; Mon, 4 Nov 2019 22:01:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572904874; bh=pTNpI8krUYYgmHKAFknIIvE6NqLq8p5eAggBhfZj+Vw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QjLcbp/uzpNM70jrUXP7xEJIFnAgWo/F0sSoIZpePPGnBmSkARfEh6GbaNAuh1Inu KnB/6e5EmekgyK6Kj2rwfzlBZvl3YNDNEV9oo6puIuL8vu42F4eqSH94oD3gFJ2oMR QCuZiB40UH6imoakEvG/yh2xB3UIjVb7r5Jnn8pQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Petr Mladek , "Steven Rostedt (VMware)" , Sasha Levin Subject: [PATCH 4.19 101/149] tracing: Initialize iter->seq after zeroing in tracing_read_pipe() Date: Mon, 4 Nov 2019 22:44:54 +0100 Message-Id: <20191104212143.566999230@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191104212126.090054740@linuxfoundation.org> References: <20191104212126.090054740@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Petr Mladek [ Upstream commit d303de1fcf344ff7c15ed64c3f48a991c9958775 ] A customer reported the following softlockup: [899688.160002] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [test.sh:16464] [899688.160002] CPU: 0 PID: 16464 Comm: test.sh Not tainted 4.12.14-6.23-azure #1 SLE12-SP4 [899688.160002] RIP: 0010:up_write+0x1a/0x30 [899688.160002] Kernel panic - not syncing: softlockup: hung tasks [899688.160002] RIP: 0010:up_write+0x1a/0x30 [899688.160002] RSP: 0018:ffffa86784d4fde8 EFLAGS: 00000257 ORIG_RAX: ffffffffffffff12 [899688.160002] RAX: ffffffff970fea00 RBX: 0000000000000001 RCX: 0000000000000000 [899688.160002] RDX: ffffffff00000001 RSI: 0000000000000080 RDI: ffffffff970fea00 [899688.160002] RBP: ffffffffffffffff R08: ffffffffffffffff R09: 0000000000000000 [899688.160002] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8b59014720d8 [899688.160002] R13: ffff8b59014720c0 R14: ffff8b5901471090 R15: ffff8b5901470000 [899688.160002] tracing_read_pipe+0x336/0x3c0 [899688.160002] __vfs_read+0x26/0x140 [899688.160002] vfs_read+0x87/0x130 [899688.160002] SyS_read+0x42/0x90 [899688.160002] do_syscall_64+0x74/0x160 It caught the process in the middle of trace_access_unlock(). There is no loop. So, it must be looping in the caller tracing_read_pipe() via the "waitagain" label. Crashdump analyze uncovered that iter->seq was completely zeroed at this point, including iter->seq.seq.size. It means that print_trace_line() was never able to print anything and there was no forward progress. The culprit seems to be in the code: /* reset all but tr, trace, and overruns */ memset(&iter->seq, 0, sizeof(struct trace_iterator) - offsetof(struct trace_iterator, seq)); It was added by the commit 53d0aa773053ab182877 ("ftrace: add logic to record overruns"). It was v2.6.27-rc1. It was the time when iter->seq looked like: struct trace_seq { unsigned char buffer[PAGE_SIZE]; unsigned int len; }; There was no "size" variable and zeroing was perfectly fine. The solution is to reinitialize the structure after or without zeroing. Link: http://lkml.kernel.org/r/20191011142134.11997-1-pmladek@suse.com Signed-off-by: Petr Mladek Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Sasha Levin --- kernel/trace/trace.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 27b17ea44f745..bdd7f3d78724e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5766,6 +5766,7 @@ waitagain: sizeof(struct trace_iterator) - offsetof(struct trace_iterator, seq)); cpumask_clear(iter->started); + trace_seq_init(&iter->seq); iter->pos = -1; trace_event_read_lock(); -- 2.20.1