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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 679E9C04AAF for ; Mon, 20 May 2019 05:55:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3AF8920815 for ; Mon, 20 May 2019 05:55:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730212AbfETFzn (ORCPT ); Mon, 20 May 2019 01:55:43 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:42014 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725829AbfETFzm (ORCPT ); Mon, 20 May 2019 01:55:42 -0400 Received: by mail-pl1-f196.google.com with SMTP id x15so6168019pln.9 for ; Sun, 19 May 2019 22:55:42 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=rG3c0xkdVvjC04ApwJQuMwZR/e4oemfgtIYmPM9Dho0=; b=kWHmSi2RIhH46sljfwqmszy+1DGoJjQpOvGOSsz+Thk5leljI1kuqmkVL1HrzqRh2P wJF5WQKK5V+pNWnMNgoi14T+DVzFWax87OfhfzP5kHaflmazPtFBbTM/YnW7ZyJ18G2+ wo0k17zHTxvf/kmOvgscBccvmyZULamX7a2eRc9eTTZ08/6/b3cdM2hDDVGFu1LG7R3I oqPZnJM2Umbq24uB9NBhfa1RdEl9DSg7AZeQEm7B//ybR+zmlAVSB685wTIQ/B0d/s1k IktfDTZTCT9xT12/PJ9UeNhR3z55vK0f8vQjF2pODcngmC3P7iyBmmlv/tGJrIUx/RG3 7daQ== X-Gm-Message-State: APjAAAU8G/RgoWGW+OlRYlDruVN9//+3Y7GZnpDuhjTvUNd0sbD2LU4F vdeAcsxe9kVhn+00Mp1nFJ7ETdBzj8E= X-Google-Smtp-Source: APXvYqxbKEJ45oGZXOPGTuLMSU/8vX87ERRH8Fci9NzJJBt7aHURs7Hh9UeScppNXZKGPbhpcnD+Cw== X-Received: by 2002:a17:902:7082:: with SMTP id z2mr50701635plk.176.1558331742116; Sun, 19 May 2019 22:55:42 -0700 (PDT) Received: from localhost.localdomain ([122.177.184.216]) by smtp.gmail.com with ESMTPSA id d15sm49144449pfm.186.2019.05.19.22.55.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 19 May 2019 22:55:41 -0700 (PDT) Subject: Re: [RFC PATCH] vmcore: Add a kernel cmdline device_dump_limit To: Kairui Song Cc: Linux Kernel Mailing List , "kexec@lists.infradead.org" , "David S . Miller" , Rahul Lakkireddy , Eric Biederman , Andrew Morton , Dave Young , Alexey Dobriyan , Ganesh Goudar References: <20190510102051.25647-1-kasong@redhat.com> <4f453ec6-67a6-2c8f-2aab-acb54ae55645@redhat.com> From: Bhupesh Sharma Message-ID: <1b170096-b47b-2178-b27a-c4ec351f564d@redhat.com> Date: Mon, 20 May 2019 11:25:36 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/16/2019 01:49 PM, Kairui Song wrote: > On Fri, May 10, 2019 at 7:17 PM Bhupesh Sharma wrote: >> >> Hi Kairui, >> >> Thanks for the patch. Please see my comments in-line: >> >> On 05/10/2019 03:50 PM, Kairui Song wrote: >>> Device dump allow drivers to add device related dump data to vmcore as >>> they want. This have a potential issue, the data is stored in memory, >>> drivers may append too much data and use too much memory. The vmcore is >>> typically used in a kdump kernel which runs in a pre-reserved small >>> chunk of memory. So as a result it will make kdump unusable at all due >>> to OOM issues. >>> >>> So introduce new device_dump_limit= kernel parameter, and set the >>> default limit to 0, so device dump is not enabled unless user specify >>> the accetable maxiam >> >> ^^^^ acceptable maximum > > Will fix this typo. Ok. >>> memory usage for device dump data. In this way user >>> will also have the chance to adjust the kdump reserved memory >>> accordingly. >> >> Hmmm., this doesn't give much confidence with the >> PROC_VMCORE_DEVICE_DUMP feature in its current shape. Rather shouldn't >> we be enabling config PROC_VMCORE_DEVICE_DUMP only under EXPERT mode for >> now, considering that this feature needs further thrashing and testing >> with real setups including platforms where drivers append large amounts >> of data to vmcore: > > I think no need to move it to expert mode, just leave it disabled by > default should be better, that should be enough to make sure driver > won't append that much memory and cause OOM, while it could still be > enabled without changing the kernel, so this feature won't bring extra > risk, and could be enabled anytime easily. I have seen some arm64 users report issues on mailing lists with PROC_VMCORE_DEVICE_DUMP enabled as this causes frequent OOM in the arm64 crash dump kernel. I think they are using this infrastructure to extend/enable device driver debugging on some arm64 platforms and finding issues with the crash dump kernel. I will do some analysis later-on (when I get some spare time) and post a patch (if needed) to put the same under EXPERT mode for now. >> diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig >> index 817c02b13b1d..c47a12cf7fc0 100644 >> --- a/fs/proc/Kconfig >> +++ b/fs/proc/Kconfig >> @@ -45,7 +45,7 @@ config PROC_VMCORE >> Exports the dump image of crashed kernel in ELF format. >> >> config PROC_VMCORE_DEVICE_DUMP >> - bool "Device Hardware/Firmware Log Collection" >> + bool "Device Hardware/Firmware Log Collection" if EXPERT >> depends on PROC_VMCORE >> default n >> help >> @@ -59,6 +59,12 @@ config PROC_VMCORE_DEVICE_DUMP >> If you say Y here, the collected device dumps will be added >> as ELF notes to /proc/vmcore. >> >> + Considering that there can be device drivers which append >> + large amounts of data to vmcore, you should say N here unless >> + you are reserving a large chunk of memory for crashdump >> + kernel, because otherwise the crashdump kernel might become >> + unusable due to OOM issues. >> + >> >> May be you can add a 'Fixes:' tag here. > > Problem is previous commit seems not broken, just bring extra memory > stress. Is "Fixes:" tag suitable for this commit? I think since the earlier patch causes an OOM, it would be better to atleast mention it in the git log (for easier git bisect later on). If not the 'Fixes:' tag may be we can use a 'Since commit ..' like wording in the commit log. >>> Signed-off-by: Kairui Song >>> --- >>> fs/proc/vmcore.c | 20 ++++++++++++++++++++ >>> 1 file changed, 20 insertions(+) >>> >>> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c >>> index 3fe90443c1bb..e28695ef2439 100644 >>> --- a/fs/proc/vmcore.c >>> +++ b/fs/proc/vmcore.c >>> @@ -53,6 +53,9 @@ static struct proc_dir_entry *proc_vmcore; >>> /* Device Dump list and mutex to synchronize access to list */ >>> static LIST_HEAD(vmcoredd_list); >>> static DEFINE_MUTEX(vmcoredd_mutex); >>> + >>> +/* Device Dump Limit */ >>> +static size_t vmcoredd_limit; >>> #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */ >>> >>> /* Device Dump Size */ >>> @@ -1465,6 +1468,11 @@ int vmcore_add_device_dump(struct vmcoredd_data *data) >>> data_size = roundup(sizeof(struct vmcoredd_header) + data->size, >>> PAGE_SIZE); >>> >>> + if (vmcoredd_orig_sz + data_size >= vmcoredd_limit) { >>> + ret = -ENOMEM; >> >> Should we be adding a WARN() here to let the user know that the device >> dump data will not be available in vmcore? > > Yes, that could be very helpful. How about pr_err_once? WARN is too > noise, just give a hint to the user that device dump is disabled > should be enough, so user will know why device dump data is not > present and will just enable it. Sure, pr_err() should be OK as well. >>> + goto out_err; >>> + } >>> + >>> /* Allocate buffer for driver's to write their dumps */ >>> buf = vmcore_alloc_buf(data_size); >>> if (!buf) { >>> @@ -1502,6 +1510,18 @@ int vmcore_add_device_dump(struct vmcoredd_data *data) >>> return ret; >>> } >>> EXPORT_SYMBOL(vmcore_add_device_dump); >>> + >>> +static int __init parse_vmcoredd_limit(char *arg) >>> +{ >>> + char *end; >>> + >>> + if (!arg) >>> + return -EINVAL; >>> + vmcoredd_limit = memparse(arg, &end); >>> + return end > arg ? 0 : -EINVAL; >>> + >>> +} >>> +__setup("device_dump_limit=", parse_vmcoredd_limit); >> >> We should be adding this boot argument and its description to >> 'Documentation/admin-guide/kernel-parameters.txt' > > Good suggestion, will update the document. > >> >>> #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */ >>> >>> /* Free all dumps in vmcore device dump list */ >>> Thanks, Bhupesh