From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f175.google.com (mail-wi0-f175.google.com [209.85.212.175]) by kanga.kvack.org (Postfix) with ESMTP id BEC9D6B025D for ; Mon, 21 Sep 2015 10:06:19 -0400 (EDT) Received: by wicge5 with SMTP id ge5so117573951wic.0 for ; Mon, 21 Sep 2015 07:06:19 -0700 (PDT) Received: from mail-wi0-f173.google.com (mail-wi0-f173.google.com. [209.85.212.173]) by mx.google.com with ESMTPS id lk9si17401261wic.92.2015.09.21.07.06.18 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 21 Sep 2015 07:06:18 -0700 (PDT) Received: by wicfx3 with SMTP id fx3so113082228wic.0 for ; Mon, 21 Sep 2015 07:06:18 -0700 (PDT) Date: Mon, 21 Sep 2015 17:06:15 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] fs: fix data race on mnt.mnt_flags Message-ID: <20150921140615.GA30755@node.dhcp.inet.fi> References: <1442837807-70839-1-git-send-email-dvyukov@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1442837807-70839-1-git-send-email-dvyukov@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, riel@redhat.com, mhocko@suse.cz, oleg@redhat.com, sasha.levin@oracle.com, gang.chen.5i5j@gmail.com, pfeiner@google.com, aarcange@redhat.com, vishnu.ps@samsung.com, linux-mm@kvack.org, glider@google.com, kcc@google.com, andreyknvl@google.com, ktsan@googlegroups.com, paulmck@linux.vnet.ibm.com On Mon, Sep 21, 2015 at 02:16:47PM +0200, Dmitry Vyukov wrote: > do_remount() does: > > mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK; > mnt->mnt.mnt_flags = mnt_flags; > > This can easily be compiled as: > > mnt->mnt.mnt_flags &= ~MNT_USER_SETTABLE_MASK; > mnt->mnt.mnt_flags |= mnt_flags; > > (also 2 memory accesses, less register pressure) > The flags are being concurrently read by e.g. do_mmap_pgoff() > which does: > > if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) > > As the result we can allow to mmap a MNT_NOEXEC mount > as VM_EXEC. > > Use WRITE_ONCE() to set new flags. > > The data race was found with KernelThreadSanitizer (KTSAN). > > Signed-off-by: Dmitry Vyukov Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org