From patchwork Tue Aug 10 17:30:32 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 495873 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=-19.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT 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 EEB62C19F40 for ; Tue, 10 Aug 2021 17:39:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C417D61244 for ; Tue, 10 Aug 2021 17:39:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233709AbhHJRkK (ORCPT ); Tue, 10 Aug 2021 13:40:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:43106 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235081AbhHJRjT (ORCPT ); Tue, 10 Aug 2021 13:39:19 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 32946610A0; Tue, 10 Aug 2021 17:36:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1628617013; bh=RABCGUc/EXegW3+JRJjZfkZkcxe79Tvl1euXjL0Bkp0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ItW/PH5GXADg6/fBnOC/gdHxbysdKQiNRz8KsTBLJsi23jW5M+cvvrr2fX85OPQIz X2EVpnU97WKqgxeax3Ju7so0wby2C0Uryks0Zs8hEpD7oO0lXrZxxcW9bo37Vutzel eI5zyy6G/IzDVkM9lW+Tp/Nnu7Mbl0lLCuZr+euw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Alex Xu (Hello71)" , Linus Torvalds Subject: [PATCH 5.4 59/85] pipe: increase minimum default pipe size to 2 pages Date: Tue, 10 Aug 2021 19:30:32 +0200 Message-Id: <20210810172950.227398327@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210810172948.192298392@linuxfoundation.org> References: <20210810172948.192298392@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Alex Xu (Hello71) commit 46c4c9d1beb7f5b4cec4dd90e7728720583ee348 upstream. This program always prints 4096 and hangs before the patch, and always prints 8192 and exits successfully after: int main() { int pipefd[2]; for (int i = 0; i < 1025; i++) if (pipe(pipefd) == -1) return 1; size_t bufsz = fcntl(pipefd[1], F_GETPIPE_SZ); printf("%zd\n", bufsz); char *buf = calloc(bufsz, 1); write(pipefd[1], buf, bufsz); read(pipefd[0], buf, bufsz-1); write(pipefd[1], buf, 1); } Note that you may need to increase your RLIMIT_NOFILE before running the program. Fixes: 759c01142a ("pipe: limit the per-user amount of pages allocated in pipes") Cc: Link: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/ Link: https://lore.kernel.org/lkml/1628127094.lxxn016tj7.none@localhost/ Signed-off-by: Alex Xu (Hello71) Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/pipe.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) --- a/fs/pipe.c +++ b/fs/pipe.c @@ -31,6 +31,21 @@ #include "internal.h" /* + * New pipe buffers will be restricted to this size while the user is exceeding + * their pipe buffer quota. The general pipe use case needs at least two + * buffers: one for data yet to be read, and one for new data. If this is less + * than two, then a write to a non-empty pipe may block even if the pipe is not + * full. This can occur with GNU make jobserver or similar uses of pipes as + * semaphores: multiple processes may be waiting to write tokens back to the + * pipe before reading tokens: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/. + * + * Users can reduce their pipe buffers with F_SETPIPE_SZ below this at their + * own risk, namely: pipe writes to non-full pipes may block until the pipe is + * emptied. + */ +#define PIPE_MIN_DEF_BUFFERS 2 + +/* * The max size that a non-root user is allowed to grow the pipe. Can * be set by root in /proc/sys/fs/pipe-max-size */ @@ -666,8 +681,8 @@ struct pipe_inode_info *alloc_pipe_info( user_bufs = account_pipe_buffers(user, 0, pipe_bufs); if (too_many_pipe_buffers_soft(user_bufs) && is_unprivileged_user()) { - user_bufs = account_pipe_buffers(user, pipe_bufs, 1); - pipe_bufs = 1; + user_bufs = account_pipe_buffers(user, pipe_bufs, PIPE_MIN_DEF_BUFFERS); + pipe_bufs = PIPE_MIN_DEF_BUFFERS; } if (too_many_pipe_buffers_hard(user_bufs) && is_unprivileged_user())