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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 1D05AC43387 for ; Thu, 20 Dec 2018 12:57:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4FA321741 for ; Thu, 20 Dec 2018 12:57:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1545310653; bh=zahJAHSTs2dZhR0xFNoyWPBP+1QzrnPyPJasnmzQjEI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=lJQ73R/lZbTj9qqnNCLWACTVmvxCgFITeLbH5V0kuojQL99VpytTOY6UY6SO8y5dD TSDbmPqIciYdJnEPEQOQzxxznCIbexaPa7WELfbp4K1YGgLmXn3ANnritX6KSBVFe7 skFeEBrfHF32jGAkB7JUd0uKeaKDLUEIFBk/jajc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732209AbeLTM5d (ORCPT ); Thu, 20 Dec 2018 07:57:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:33086 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729731AbeLTM5d (ORCPT ); Thu, 20 Dec 2018 07:57:33 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 2D87AACA4; Thu, 20 Dec 2018 12:57:31 +0000 (UTC) Date: Thu, 20 Dec 2018 13:57:30 +0100 From: Michal Hocko To: Vineet Gupta Cc: linux-snps-arc@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH 1/2] ARC: show_regs: avoid page allocator Message-ID: <20181220125730.GA17350@dhcp22.suse.cz> References: <1545159239-30628-1-git-send-email-vgupta@synopsys.com> <1545159239-30628-2-git-send-email-vgupta@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1545159239-30628-2-git-send-email-vgupta@synopsys.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 18-12-18 10:53:58, Vineet Gupta wrote: > Use on-stack smaller buffers instead of dynamic pages. > > The motivation for this change was to address lockdep splat when > signal handling code calls show_regs (with preemption disabled) and > ARC show_regs calls into sleepable page allocator. > > | potentially unexpected fatal signal 11. > | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317 > | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv > | no locks held by segv/57. > | Preemption disabled at: > | [<8182f17e>] get_signal+0x4a6/0x7c4 > | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23 > | > | Stack Trace: > | arc_unwind_core.constprop.1+0xd0/0xf4 > | __might_sleep+0x1f6/0x234 > | __get_free_pages+0x174/0xca0 > | show_regs+0x22/0x330 > | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable() > | do_signal+0x30/0x224 > | resume_user_mode_begin+0x90/0xd8 > > Despite this, lockdep still barfs (see next change), but this patch > still has merit as in we use smaller/localized buffers now and there's > less instructoh trace to sift thru when debugging pesky issues. But show_regs is called from contexts which might be called from deep call chains (e.g WARN). Is it safe to allocate such a large stack there? -- Michal Hocko SUSE Labs