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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 AB9D0C433DF for ; Tue, 19 May 2020 18:46:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 548D920758 for ; Tue, 19 May 2020 18:46:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="r3DKwbpa" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 548D920758 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A7E4780012; Tue, 19 May 2020 14:46:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A0715900002; Tue, 19 May 2020 14:46:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8F68F80012; Tue, 19 May 2020 14:46:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0036.hostedemail.com [216.40.44.36]) by kanga.kvack.org (Postfix) with ESMTP id 74C22900002 for ; Tue, 19 May 2020 14:46:51 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 2A0AD4DC3 for ; Tue, 19 May 2020 18:46:51 +0000 (UTC) X-FDA: 76834350222.04.rail47_18ef9b53ab2e X-HE-Tag: rail47_18ef9b53ab2e X-Filterd-Recvd-Size: 3349 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Tue, 19 May 2020 18:46:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=TfqaqqY6RfR3+DZfCY7Gxv00z/xXVrR5qOfi/Vh95qU=; b=r3DKwbpaQwnjfQhWDApMKJ7zGt SA+i7OcPGQV30E+o+F/T750UNlEqYtmxTmwUKsYvoS7fo4xwD6gRgXHGRdQuGyFYgcxajcuYB7uA1 fJJXeX7RF9mfjvSLkbxMevTeV84sJRPWBuvdqwqGmOVPu9g/+aFFi0K10sy+nd2/0ZgZxOu+kBDZl xeByOPe8bOBhBZf7FCBkNJVH7Cd+r0I834GPLh5BP+NfAgFQT4zSSvlU3S3WuBB7PL+SeMIGOQWZO TE3A5TPXhg9NtpzqVWglD5eRKy9qMTocOuFedoqF8Io2HkXO/UDUw7b902wE0xUjh94BI2G2lbCLA yk/dDfaA==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jb7G6-0004Rz-7u; Tue, 19 May 2020 18:46:34 +0000 Date: Tue, 19 May 2020 11:46:34 -0700 From: Matthew Wilcox To: Dan Williams Cc: gregkh@linuxfoundation.org, Arnd Bergmann , Ingo Molnar , Kees Cook , Russell King , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] /dev/mem: Revoke mappings when a driver claims the region Message-ID: <20200519184634.GZ16070@bombadil.infradead.org> References: <158987153989.4000084.17143582803685077783.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <158987153989.4000084.17143582803685077783.stgit@dwillia2-desk3.amr.corp.intel.com> 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 Tue, May 19, 2020 at 12:03:06AM -0700, Dan Williams wrote: > +void revoke_devmem(struct resource *res) > +{ > + struct inode *inode = READ_ONCE(devmem_inode); > + > + /* > + * Check that the initialization has completed. Losing the race > + * is ok because it means drivers are claiming resources before > + * the fs_initcall level of init and prevent /dev/mem from > + * establishing mappings. > + */ > + smp_rmb(); > + if (!inode) > + return; Which wmb() is this pairing with? > +static int devmem_init_inode(void) > +{ > + static struct vfsmount *devmem_vfs_mount; > + static int devmem_fs_cnt; > + struct inode *inode; > + int rc; > + > + rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt); > + if (rc < 0) { > + pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc); > + return rc; > + } > + > + inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb); > + if (IS_ERR(inode)) { > + rc = PTR_ERR(inode); > + pr_err("Cannot allocate inode for /dev/mem: %d\n", rc); > + simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt); > + return rc; > + } > + > + /* publish /dev/mem initialized */ > + WRITE_ONCE(devmem_inode, inode); > + smp_wmb(); > + > + return 0; ... is that this one? I don't see what it's guarding against. Surely if it's needed to ensure that the writes to 'inode' have happened before the write of the inode pointer, the smp_wmb() needs to be before the WRITE_ONCE, not after it?