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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_MED,USER_IN_DEF_DKIM_WL 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 16E75C282DD for ; Thu, 23 May 2019 14:32:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB6F62175B for ; Thu, 23 May 2019 14:32:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="BCy6Okmk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730903AbfEWOcl (ORCPT ); Thu, 23 May 2019 10:32:41 -0400 Received: from mail-ot1-f68.google.com ([209.85.210.68]:33218 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730818AbfEWOcl (ORCPT ); Thu, 23 May 2019 10:32:41 -0400 Received: by mail-ot1-f68.google.com with SMTP id 66so5636151otq.0 for ; Thu, 23 May 2019 07:32:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=UmCv77ojMXG+c1Fp7DLXkEEMvKlYSuA0abYrccWopi8=; b=BCy6Okmk8ktr4nwvd4MspoIxsNlhMgBNgut3lK3gji1Mo8ZK86sDQuXYRAM0aEzKt1 l5h9Z162b8ZZvcy3+o2m7mOM8MFYONAclzGI9eGRFt+MvF5Vk7qd2XbUpuRtY3kwxigT TItqAHhT39/xzIdVfEVUYP6dbydvV9umwbP2vl+FxdLXFLSb9ACpWUQrIu3LG0CJGus3 efSiM9X4tBhY2RglIlFRNgfOwB840H3gEzgClahgzgTog6Yv+6has8aNNHrrbEHD2p91 f4b1gS1SqBJkPyuKpLmeXF29Yw4PJv/H5cHfQKgbABzZI5vn49C4VG2ZQkov7h619lB0 cONg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=UmCv77ojMXG+c1Fp7DLXkEEMvKlYSuA0abYrccWopi8=; b=RiFOsa9E4XM+QadpFNc6RSlpyaIoR0cKi5yjZdl67pzFS7iI3tGf/bcBNUweItjyUY a/EmTRr7QuzGas8v/dM/cVZKondqyE4xp6GbJ2B8lpfBHEEMPfIaxDw5Ov9yOVYV+7MO Iienwqu+6Nh7nPoQ3TwJHSE/4rSZve45uB7YAazsAURuWLGIT+TEaxjFPwvM4yJkl9wp jwabkbW4+HS+TOdHGHWQ0NJwofejEKHDVeky9H614+PQUswnDpTibwRL0Im+QDXMRbUM Z/8Cww+qLfOdnMOaBdEUR7P2hw3hFJypmQ/RNB22mMRO/sBDWHrdM3QTUhh9K+bgV2Q/ nj4w== X-Gm-Message-State: APjAAAXTR/Cz+BmGmiJ33QceLv2v8CTZcyZzEdJYEXXyIWLojma9DFt1 7umLMOeCMZfhvHHdSJIzmWOBbqE4AAF9Al4b7QywaQ== X-Google-Smtp-Source: APXvYqzFh/C6cDrkSdzIHZQLhSVRwEaU4gGSzclCCpHMgWTGugVQoxN/zVlngGYGKq3CVngNXUCDkIhtZyPn6qxtEko= X-Received: by 2002:a9d:7f8b:: with SMTP id t11mr72319otp.110.1558621960440; Thu, 23 May 2019 07:32:40 -0700 (PDT) MIME-Version: 1.0 References: <20190522155259.11174-1-christian@brauner.io> <20190522165737.GC4915@redhat.com> <20190523115118.pmscbd6kaqy37dym@brauner.io> In-Reply-To: <20190523115118.pmscbd6kaqy37dym@brauner.io> From: Jann Horn Date: Thu, 23 May 2019 16:32:14 +0200 Message-ID: Subject: Re: [PATCH v1 1/2] open: add close_range() To: Christian Brauner Cc: Oleg Nesterov , Al Viro , kernel list , linux-fsdevel , Linux API , Linus Torvalds , Florian Weimer , Thomas Gleixner , Arnd Bergmann , Shuah Khan , David Howells , Todd Kjos , "Dmitry V. Levin" , Miklos Szeredi , linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390 , linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch , "open list:KERNEL SELFTEST FRAMEWORK" , "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Thu, May 23, 2019 at 1:51 PM Christian Brauner wrote: [...] > I kept it dumb and was about to reply that your solution introduces more > code when it seemed we wanted to keep this very simple for now. > But then I saw that find_next_opened_fd() already exists as > find_next_fd(). So it's actually not bad compared to what I sent in v1. > So - with some small tweaks (need to test it and all now) - how do we > feel about?: [...] > static int __close_next_open_fd(struct files_struct *files, unsigned *curfd, unsigned maxfd) > { > struct file *file = NULL; > unsigned fd; > struct fdtable *fdt; > > spin_lock(&files->file_lock); > fdt = files_fdtable(files); > fd = find_next_fd(fdt, *curfd); find_next_fd() finds free fds, not used ones. > if (fd >= fdt->max_fds || fd > maxfd) > goto out_unlock; > > file = fdt->fd[fd]; > rcu_assign_pointer(fdt->fd[fd], NULL); > __put_unused_fd(files, fd); You can't do __put_unused_fd() if the old pointer in fdt->fd[fd] was NULL - because that means that the fd has been reserved by another thread that is about to put a file pointer in there, and if you release the fd here, that messes up the refcounting (or hits the BUG_ON() in __fd_install()). > out_unlock: > spin_unlock(&files->file_lock); > > if (!file) > return -EBADF; > > *curfd = fd; > filp_close(file, files); > return 0; > } > > int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd) > { > if (fd > max_fd) > return -EINVAL; > > while (fd <= max_fd) { Note that with a pattern like this, you have to be careful about what happens if someone gives you max_fd==0xffffffff - then this condition is always true and the loop can not terminate this way. > if (__close_next_fd(files, &fd, maxfd)) > break; (obviously it can still terminate this way) > cond_resched(); > fd++; > } > > return 0; > }