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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 845D1C19759 for ; Thu, 1 Aug 2019 07:52:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F4F3206A2 for ; Thu, 1 Aug 2019 07:52:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730501AbfHAHwn convert rfc822-to-8bit (ORCPT ); Thu, 1 Aug 2019 03:52:43 -0400 Received: from mx1.mail.vl.ru ([80.92.161.250]:36942 "EHLO mx1.mail.vl.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725790AbfHAHwm (ORCPT ); Thu, 1 Aug 2019 03:52:42 -0400 Received: from localhost (unknown [127.0.0.1]) by mx1.mail.vl.ru (Postfix) with ESMTP id 350EA18414AF; Thu, 1 Aug 2019 07:52:38 +0000 (UTC) X-Virus-Scanned: amavisd-new at mail.vl.ru Received: from mx1.mail.vl.ru ([127.0.0.1]) by localhost (smtp1.srv.loc [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id rbF6xbNrQuL0; Thu, 1 Aug 2019 17:52:36 +1000 (+10) Received: from [10.125.1.12] (unknown [109.126.62.18]) (Authenticated sender: turchanov@vl.ru) by mx1.mail.vl.ru (Postfix) with ESMTPSA id B91B91841490; Thu, 1 Aug 2019 17:52:36 +1000 (+10) Subject: Re: [BUG] lseek on /proc/meminfo is broken in 4.19.59 To: Gao Xiang Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <3bd775ab-9e31-c6b3-374e-7a9982a9a8cd@farpost.com> <5c4c0648-2a96-4132-9d22-91c22e7c7d4d@huawei.com> From: Sergei Turchanov Organization: FarPost Message-ID: <9e0b13fb-8355-0430-557d-6b67e2ba2aac@farpost.com> Date: Thu, 1 Aug 2019 17:52:36 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <5c4c0648-2a96-4132-9d22-91c22e7c7d4d@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Thank you very much for your suggestion. Will certainly do that. With best regards, Sergei. On 01.08.2019 17:11, Gao Xiang wrote: > Hi, > > I just took a glance, maybe due to > commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") > > I simply reverted it just now and it seems fine... but I haven't digged into this commit. > > Maybe you could Cc NeilBrown for some more advice and > I have no idea whether it's an expected behavior or not... > > Thanks, > Gao Xiang > > On 2019/8/1 14:16, Sergei Turchanov wrote: >> Hello! >> >> (I sent this e-mail two weeks ago with no feedback. Does anyone care? Wrong mailing list? Anything....?) >> >> Seeking (to an offset within file size) in /proc/meminfo is broken in 4.19.59. It does seek to a desired position, but reading from that position returns the remainder of file and then a whole copy of file. This doesn't happen with /proc/vmstat or /proc/self/maps for example. >> >> Seeking did work correctly in kernel 4.14.47. So it seems something broke in the way. >> >> Background: this kind of access pattern (seeking to /proc/meminfo) is used by libvirt-lxc fuse driver for virtualized view of /proc/meminfo. So that /proc/meminfo is broken in guests when running kernel 4.19.x. >> >> $ ./test /proc/meminfo 0        # Works as expected >> >> MemTotal:       394907728 kB >> MemFree:        173738328 kB >> ... >> DirectMap2M:    13062144 kB >> DirectMap1G:    390070272 kB >> >> ----------------------------------------------------------------------- >> >> $ ./test 1024                   # returns a copy of file after the remainder >> >> Will seek to 1024 >> >> >> Data read at offset 1024 >> gePages:         0 kB >> ShmemHugePages:        0 kB >> ShmemPmdMapped:        0 kB >> HugePages_Total:       0 >> HugePages_Free:        0 >> HugePages_Rsvd:        0 >> HugePages_Surp:        0 >> Hugepagesize:       2048 kB >> Hugetlb:               0 kB >> DirectMap4k:      245204 kB >> DirectMap2M:    13062144 kB >> DirectMap1G:    390070272 kB >> MemTotal:       394907728 kB >> MemFree:        173738328 kB >> MemAvailable:   379989680 kB >> Buffers:          355812 kB >> Cached:         207216224 kB >> ... >> DirectMap2M:    13062144 kB >> DirectMap1G:    390070272 kB >> >> As you see, after "DirectMap1G:" line, a whole copy of /proc/meminfo returned by "read". >> >> Test program: >> >> #include >> #include >> #include >> #include >> #include >> #include >> >> #define SIZE 1024 >> char buf[SIZE + 1]; >> >> int main(int argc, char *argv[]) { >>     int     fd; >>     ssize_t rd; >>     off_t   ofs = 0; >> >>     if (argc < 2) { >>         printf("Usage: test []\n"); >>         exit(1); >>     } >> >>     if (-1 == (fd = open(argv[1], O_RDONLY))) { >>         perror("open failed"); >>         exit(1); >>     } >> >>     if (argc > 2) { >>         ofs = atol(argv[2]); >>     } >>     printf("Will seek to %ld\n", ofs); >> >>     if (-1 == (lseek(fd, ofs, SEEK_SET))) { >>         perror("lseek failed"); >>         exit(1); >>     } >> >>     for (;; ofs += rd) { >>         printf("\n\nData read at offset %ld\n", ofs); >>         if (-1 == (rd = read(fd, buf, SIZE))) { >>             perror("read failed"); >>             exit(1); >>         } >>         buf[rd] = '\0'; >>         printf(buf); >>         if (rd < SIZE) { >>             break; >>         } >>     } >> >>     return 0; >> } >> >> >>