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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E202C433EF for ; Fri, 5 Nov 2021 23:57:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BB4BC60F5A for ; Fri, 5 Nov 2021 23:57:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org BB4BC60F5A Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=rere.qmqm.pl Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 309E6940020; Fri, 5 Nov 2021 19:57:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2B92894000D; Fri, 5 Nov 2021 19:57:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1A947940020; Fri, 5 Nov 2021 19:57:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 0DCB594000D for ; Fri, 5 Nov 2021 19:57:19 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B86E4182DA4AA for ; Fri, 5 Nov 2021 23:57:18 +0000 (UTC) X-FDA: 78776540598.01.6156E88 Received: from rere.qmqm.pl (rere.qmqm.pl [91.227.64.183]) by imf24.hostedemail.com (Postfix) with ESMTP id E77CBB0000B0 for ; Fri, 5 Nov 2021 23:57:17 +0000 (UTC) Received: from remote.user (localhost [127.0.0.1]) by rere.qmqm.pl (Postfix) with ESMTPSA id 4HmHVb6HGFzBs; Sat, 6 Nov 2021 00:57:11 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=rere.qmqm.pl; s=1; t=1636156635; bh=m5pndQqsZAfsS+FW1lbAnLViWscX+7vW/HS+H4mYBKg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hhhHpB7ZS4HG39gN9VN9s41HVGTMpArfwk+CIFrRRUhAAn2nVMgZajsgWsAEvJ5Uh E5kVQtH50Hw+vS/SQw2R4N2aAeNeaQxjqX7ir5sEPslX0+QLwnK90B76F+LeCC0oAQ PIxCMskP3Gv3nwVt/hQmWgI+O03uONbc4LfkN9p5SDeJJBZ6ZRwwme7leUxbDszrVm dEbpNMH+ZwjXs15naK6R98AzrEPJWYY5dGiGyLyQtkGFN9d/rjaiicUDQ2N/I12qdE 3ePV/0GKFuuOK26dKbitWlt3+bMzUazhaKZ5rx7dILwSez6IuMQDIpnakNB9l+ZBGt /qCnycePN9fPQ== X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.3 at mail Date: Sat, 6 Nov 2021 00:57:06 +0100 From: =?iso-8859-2?Q?Micha=B3_Miros=B3aw?= To: Yafang Shao Cc: Andrew Morton , Kees Cook , Steven Rostedt , Mathieu Desnoyers , Arnaldo Carvalho de Melo , Petr Mladek , Peter Zijlstra , Al Viro , Valentin Schneider , Qiang Zhang , robdclark , christian , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Vincent Guittot , David Miller , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin Lau , Song Liu , Yonghong Song , john fastabend , KP Singh , dennis.dalessandro@cornelisnetworks.com, mike.marciniszyn@cornelisnetworks.com, dledford@redhat.com, jgg@ziepe.ca, linux-rdma@vger.kernel.org, netdev , bpf , "linux-perf-use." , linux-fsdevel@vger.kernel.org, Linux MM , LKML , kernel test robot , kbuild test robot Subject: Re: [PATCH v7 00/11] extend task comm from 16 to 24 Message-ID: References: <20211101060419.4682-1-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-2 Content-Disposition: inline In-Reply-To: Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=rere.qmqm.pl header.s=1 header.b=hhhHpB7Z; spf=pass (imf24.hostedemail.com: domain of mirq-linux@rere.qmqm.pl designates 91.227.64.183 as permitted sender) smtp.mailfrom=mirq-linux@rere.qmqm.pl; dmarc=pass (policy=reject) header.from=rere.qmqm.pl X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: E77CBB0000B0 X-Stat-Signature: 9aubyirp3hzsnyh5ur165zhd5jyiifn3 X-HE-Tag: 1636156637-515148 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Nov 05, 2021 at 02:34:58PM +0800, Yafang Shao wrote: > On Thu, Nov 4, 2021 at 9:37 AM Micha=B3 Miros=B3aw wrote: > > > > On Mon, Nov 01, 2021 at 06:04:08AM +0000, Yafang Shao wrote: > > > There're many truncated kthreads in the kernel, which may make trou= ble > > > for the user, for example, the user can't get detailed device > > > information from the task comm. > > > > > > This patchset tries to improve this problem fundamentally by extend= ing > > > the task comm size from 16 to 24, which is a very simple way. > > [...] > > > > Hi, > > > > I've tried something like this a few years back. My attempt got mostl= y > > lost in the mailing lists, but I'm still carrying the patches in my > > tree [1]. My target was userspace thread names, and it turned out mor= e > > involved than I had time for. > > > > [1] https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D2c3814268caf2b= 1fee6d1a0b61fd1730ce135d4a > > and its parents > > >=20 > Hi Michal, >=20 > Thanks for the information. >=20 > I have looked through your patches. It seems to contain six patches > now and can be divided into three parts per my understanding. >=20 > 1. extend task comm len > This parts contains below 4 patches: > [prctl: prepare for bigger > TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3Dcfd99= db9cf911bb4d106889aeba1dfe89b6527d0) > [bluetooth: prepare for bigger > TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3Dba280= 5f5196865b81cc6fc938ea53af2c7c2c892) > [taskstats: prepare for bigger > TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D4d29b= fedc57b36607915a0171f4864ec504908ca) > [mm: make TASK_COMM_LEN > configurable](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D362acc= 35582445174589184c738c4d86ec7d174b) >=20 > What kind of userspace issues makes you extend the task comm length ? > Why not just use /proc/[pid]/cmdline ? This was to enable longer thread names (as set by pthread_setname_np()). Currently its 16 bytes, and that's too short for e.g. Chrome's or Firefox= 'es threads. I believe that FreeBSD has 32-byte limit and so I expect that major portable code is already prepared for bigger thread names. > 2. A fix > Below patch: > [procfs: signal /proc/PID/comm write > truncation](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3Dd7202738= 8d4d95db5438a7a574e0a03ae4b5d6d7) >=20 > It seems this patch is incomplete ? I don't know what it means to do. Currently writes to /proc/PID/comm are silently truncated. This patch makes the write() call return the actual number of bytes actually written and on subsequent calls return -ENOSPC. glibc checks the length in pthread_setname_np() before write(), so the change is not currently relevant for it. I don't know/remember what other runtimes do, though. > 3. A feature provided for pthread_getname_np > Below patch: > [procfs: lseek(/proc/PID/comm, 0, > SEEK_END)](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D2c3814268= caf2b1fee6d1a0b61fd1730ce135d4a) >=20 > It seems this patch is useful. With this patch the userspace can > directly get the TASK_COMM_LEN through the API. This one I'm not really fond of because it abuses lseek() in that it doesn't move the write pointer. But in case of /proc files this normally would return EINVAL anyway. Best Regards Micha=B3=A0Miros=B3aw