From patchwork Mon Jul 1 06:20:14 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christoph Hellwig X-Patchwork-Id: 11025039 X-Patchwork-Delegate: bhelgaas@google.com Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 545011398 for ; Mon, 1 Jul 2019 06:21:37 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 55B5F28329 for ; Mon, 1 Jul 2019 06:21:37 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 49991284DA; Mon, 1 Jul 2019 06:21:37 +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=-7.7 required=2.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable 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 E3E9B28329 for ; Mon, 1 Jul 2019 06:21:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727707AbfGAGVD (ORCPT ); Mon, 1 Jul 2019 02:21:03 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:48550 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727665AbfGAGVC (ORCPT ); Mon, 1 Jul 2019 02:21:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From :Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=MFOQKdBekg4uOAbPxr4fTMLEjMHRTQOu8rr2EDfIjss=; b=almZJDAbXnBzGls3pOj8NvkNrg EDtv5JCQhprtUoj3msL+8HdfB1SF/bGw3a7VYmwkTA3dICFI4cqC6GaUuZTpYn1JfQvs8543MUZQa /cjCFY7Nb30zzkZ1LWtxW1UbEYJtXcLWKms8VR3iI42b3WG6HreqXzn/j+dgC92Bh3IT+9q76eFjs HdoS+gFfVfgE0Ik93/RTa7Pft0ZeMVk5W+f1ouhTl61ym6nAg6Lq3hqUVshyyXXLoAgViMSi61syX 4zsqcXeDSTjSDrYePaOl1SrEhHZHmGtM+ScRgoGqpBcAAWLJo17YUdU+msd/f6SA00fh++p5Z0Q+O AKbcbwVQ==; Received: from [46.140.178.35] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hhpgQ-00036S-QO; Mon, 01 Jul 2019 06:20:59 +0000 From: Christoph Hellwig To: Dan Williams , =?utf-8?b?SsOpcsO0bWUgR2xpc3Nl?= , Jason Gunthorpe , Ben Skeggs Cc: Ira Weiny , linux-mm@kvack.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-nvdimm@lists.01.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Philip Yang Subject: [PATCH 16/22] mm/hmm: Remove confusing comment and logic from hmm_release Date: Mon, 1 Jul 2019 08:20:14 +0200 Message-Id: <20190701062020.19239-17-hch@lst.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190701062020.19239-1-hch@lst.de> References: <20190701062020.19239-1-hch@lst.de> MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Jason Gunthorpe hmm_release() is called exactly once per hmm. ops->release() cannot accidentally trigger any action that would recurse back onto hmm->mirrors_sem. This fixes a use after-free race of the form: CPU0 CPU1 hmm_release() up_write(&hmm->mirrors_sem); hmm_mirror_unregister(mirror) down_write(&hmm->mirrors_sem); up_write(&hmm->mirrors_sem); kfree(mirror) mirror->ops->release(mirror) The only user we have today for ops->release is an empty function, so this is unambiguously safe. As a consequence of plugging this race drivers are not allowed to register/unregister mirrors from within a release op. Signed-off-by: Jason Gunthorpe Reviewed-by: Christoph Hellwig Tested-by: Philip Yang --- mm/hmm.c | 28 +++++++++------------------- 1 file changed, 9 insertions(+), 19 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index c30aa9403dbe..b224ea635a77 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -130,26 +130,16 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) */ WARN_ON(!list_empty_careful(&hmm->ranges)); - down_write(&hmm->mirrors_sem); - mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror, - list); - while (mirror) { - list_del_init(&mirror->list); - if (mirror->ops->release) { - /* - * Drop mirrors_sem so the release callback can wait - * on any pending work that might itself trigger a - * mmu_notifier callback and thus would deadlock with - * us. - */ - up_write(&hmm->mirrors_sem); + down_read(&hmm->mirrors_sem); + list_for_each_entry(mirror, &hmm->mirrors, list) { + /* + * Note: The driver is not allowed to trigger + * hmm_mirror_unregister() from this thread. + */ + if (mirror->ops->release) mirror->ops->release(mirror); - down_write(&hmm->mirrors_sem); - } - mirror = list_first_entry_or_null(&hmm->mirrors, - struct hmm_mirror, list); } - up_write(&hmm->mirrors_sem); + up_read(&hmm->mirrors_sem); hmm_put(hmm); } @@ -279,7 +269,7 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror) struct hmm *hmm = mirror->hmm; down_write(&hmm->mirrors_sem); - list_del_init(&mirror->list); + list_del(&mirror->list); up_write(&hmm->mirrors_sem); hmm_put(hmm); }