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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 609E7C43219 for ; Sat, 27 Apr 2019 01:52:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C7DA206BA for ; Sat, 27 Apr 2019 01:52:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556329932; bh=Oi0TxYuDHBd93kuX9fo74E5Om1hd3KEPLC7F9JU9O7k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ifrTnuSpfzsqL1LRwUSNlUkNc5IzrdmAEws5VojbyfeSiMSIVBkDqrDWh971QWtmg hMRygKbsi+kE2c/wlWPDO6PedM8hFcUUDwYrLvwx9BrRS+AVSBsfDjkZ8SMMJ2bPI0 gVMBFOTTwKo5em0hh9ZvliwZAOfjQ6gWQ8LTSgfM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728489AbfD0BwL (ORCPT ); Fri, 26 Apr 2019 21:52:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:44414 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728061AbfD0Bkm (ORCPT ); Fri, 26 Apr 2019 21:40:42 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 09CCD208CB; Sat, 27 Apr 2019 01:40:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556329241; bh=Oi0TxYuDHBd93kuX9fo74E5Om1hd3KEPLC7F9JU9O7k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jDZ8BR4FV0etFXwiRas+bHOMFvY8AODs8wusc2k1iyA7iFclmg09OYEHpnhRJwQwh sPHdWqu8NJNUKFeQliDejfZfk6LiFyqc6URhqa/Ap5Xj6GOHmWKBt1ZaGZ5VKNDPCj nQ2sRz/q91PbeeLXD66KQkbbb59mXUtTanhtl0lo= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Linus Torvalds , Jann Horn , stable@kernel.org, Sasha Levin , linux-mm@kvack.org Subject: [PATCH AUTOSEL 5.0 76/79] mm: make page ref count overflow check tighter and more explicit Date: Fri, 26 Apr 2019 21:38:35 -0400 Message-Id: <20190427013838.6596-76-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190427013838.6596-1-sashal@kernel.org> References: <20190427013838.6596-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds [ Upstream commit f958d7b528b1b40c44cfda5eabe2d82760d868c3 ] We have a VM_BUG_ON() to check that the page reference count doesn't underflow (or get close to overflow) by checking the sign of the count. That's all fine, but we actually want to allow people to use a "get page ref unless it's already very high" helper function, and we want that one to use the sign of the page ref (without triggering this VM_BUG_ON). Change the VM_BUG_ON to only check for small underflows (or _very_ close to overflowing), and ignore overflows which have strayed into negative territory. Acked-by: Matthew Wilcox Cc: Jann Horn Cc: stable@kernel.org Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- include/linux/mm.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 80bb6408fe73..541d99b86aea 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -965,6 +965,10 @@ static inline bool is_pci_p2pdma_page(const struct page *page) } #endif /* CONFIG_DEV_PAGEMAP_OPS */ +/* 127: arbitrary random number, small enough to assemble well */ +#define page_ref_zero_or_close_to_overflow(page) \ + ((unsigned int) page_ref_count(page) + 127u <= 127u) + static inline void get_page(struct page *page) { page = compound_head(page); @@ -972,7 +976,7 @@ static inline void get_page(struct page *page) * Getting a normal page or the head of a compound page * requires to already have an elevated page->_refcount. */ - VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page); + VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page); page_ref_inc(page); } -- 2.19.1