From patchwork Thu Nov 24 10:55:40 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Miklos Szeredi X-Patchwork-Id: 9445183 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 93E486075F for ; Thu, 24 Nov 2016 10:56:46 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 9D062269A3 for ; Thu, 24 Nov 2016 10:56:46 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 91F1827C14; Thu, 24 Nov 2016 10:56:46 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.4 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RCVD_IN_SORBS_SPAM autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 453EE269A3 for ; Thu, 24 Nov 2016 10:56:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964927AbcKXKz4 (ORCPT ); Thu, 24 Nov 2016 05:55:56 -0500 Received: from mail-wm0-f47.google.com ([74.125.82.47]:37429 "EHLO mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964832AbcKXKzz (ORCPT ); Thu, 24 Nov 2016 05:55:55 -0500 Received: by mail-wm0-f47.google.com with SMTP id t79so56169420wmt.0 for ; Thu, 24 Nov 2016 02:55:53 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=9oBGRxEwPsC+bmul9y3A5gFpKOJ0HXo6Ibr3NqkzQks=; b=GzKcwG4MF0jhcXPX92E1WJGhSWhMjye4JJc8lCSlEOs9Jf5IdQtGV1is5zQ1CXTvST Jlj+k15+UPsOfsvBOLC8UkPi/qfe85DgFreygjeo0souXAN6QXhtOfdNo0WYHRkm7nu4 xWC25w8imXIeVOKuCVW5Fq+KdJwfzRXWxZXky/eRz3rd9/2g1FbEPHiEbU8GfRRovKg3 6VPSeBghqtP22b8f/5QYbVGTiL5GfJQHAn3x4I2h9qMMB+meqxovTckPXj0B3XGxI/LH NyeBONRK4zvkbD3OAS+5PHlPOsLVcjmkTZdh4azLTmFe5W+mwWtpJ6U4/FbKkxtjGoQY Lwcw== X-Gm-Message-State: AKaTC03Amt7nQ/fSfVicPTFIOqjs1eSch0F3f+SNBC9jHoXicEhW/QxyiUPcgvVrpifJUCDa X-Received: by 10.28.232.16 with SMTP id f16mr1595272wmh.103.1479984952818; Thu, 24 Nov 2016 02:55:52 -0800 (PST) Received: from veci.piliscsaba.szeredi.hu (pool-dsl-2c-0018.externet.hu. [217.173.44.24]) by smtp.gmail.com with ESMTPSA id g73sm7587416wme.16.2016.11.24.02.55.51 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Nov 2016 02:55:51 -0800 (PST) From: Miklos Szeredi To: linux-unionfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 3/7] mm: ovl: copy-up on MAP_SHARED Date: Thu, 24 Nov 2016 11:55:40 +0100 Message-Id: <1479984944-1017-5-git-send-email-mszeredi@redhat.com> X-Mailer: git-send-email 2.5.5 In-Reply-To: <1479984944-1017-1-git-send-email-mszeredi@redhat.com> References: <1479984944-1017-1-git-send-email-mszeredi@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP A corner case of a corner case is when - file opened for O_RDONLY - which is then memory mapped SHARED - file opened for O_WRONLY - contents modified - contents read back though the shared mapping Unfortunately it looks very difficult to do anything about the established shared map after the file is copied up. Instead when a read-only file is mapped shared overlayfs copies up the file before actually doing the map. This may result in unnecessary copy-ups (but so may copy-up on open(O_RDWR) for exampe). We can revisit this later if it turns out to be a performance problem in real life. Signed-off-by: Miklos Szeredi --- mm/util.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/mm/util.c b/mm/util.c index 1a41553db866..09a179f92d18 100644 --- a/mm/util.c +++ b/mm/util.c @@ -300,6 +300,28 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr, ret = security_mmap_file(file, prot, flag); if (!ret) { + /* + * Special treatment for overlayfs: + * + * Take MAP_SHARED/PROT_READ as hint about future writes to the + * file (through another file descriptor). Caller might not + * have had such an intent, but we hope MAP_PRIVATE will be used + * in most such cases. + * + * If we don't copy up now and the file is modified, it becomes + * really difficult to change the mapping to match that of the + * file's content later. + * + * Copy up needs to be done without mmap_sem since it takes vfs + * locks which would potentially deadlock under mmap_sem. + */ + if ((flag & MAP_SHARED) && !(prot & PROT_WRITE)) { + void *p = d_real(file->f_path.dentry, NULL, O_WRONLY); + + if (IS_ERR(p)) + return PTR_ERR(p); + } + if (down_write_killable(&mm->mmap_sem)) return -EINTR; ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,