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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 985B2C433F5 for ; Tue, 26 Oct 2021 19:50:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3B43960E05 for ; Tue, 26 Oct 2021 19:50:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3B43960E05 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id CC53E940008; Tue, 26 Oct 2021 15:50:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C74F2940007; Tue, 26 Oct 2021 15:50:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B64C1940008; Tue, 26 Oct 2021 15:50:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0046.hostedemail.com [216.40.44.46]) by kanga.kvack.org (Postfix) with ESMTP id AA08F940007 for ; Tue, 26 Oct 2021 15:50:48 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 6422D183F6A24 for ; Tue, 26 Oct 2021 19:50:48 +0000 (UTC) X-FDA: 78739631376.05.9E34380 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf23.hostedemail.com (Postfix) with ESMTP id 390B290000A7 for ; Tue, 26 Oct 2021 19:50:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=shc+/NvHg/NcqVmYgURHASgtGulIua8OVbhJZJMa/OY=; b=h2scTVFQCKTqaThnNi+sQi6FNf TYuSImBkJQK3rNZLy356ezVStEbL1f3qyQPUSE4tkSAPeMxKOyIKv4nFvePDmdmyEBut4m2vNTQTo EyHvTGyQaAFDe61wM8DoK+02q11vl3ypl3t6jJhFAwHb+YOdhal0Fh8bpRPRSD2QZjMyxDh1qNqli takQyvaijMoRQvZn/jVD6uy4uokCh4Oxo8yPhskgCJBbAnMZVBkST9zH03/QERLhu+Cy7/pOuQsFw hi+ZCTXpluw6yM9ekPYE68dI2gKYLwOlIGwzscTYfSy0TPkXaRRBt3cCG2lx2HQ+Nbp3Ymi3H5ywF ENeF1uXA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mfSRP-00H7SC-Jc; Tue, 26 Oct 2021 19:49:21 +0000 Date: Tue, 26 Oct 2021 20:48:59 +0100 From: Matthew Wilcox To: Pasha Tatashin Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-m68k@lists.linux-m68k.org, anshuman.khandual@arm.com, akpm@linux-foundation.org, william.kucharski@oracle.com, mike.kravetz@oracle.com, vbabka@suse.cz, geert@linux-m68k.org, schmitzmic@gmail.com, rostedt@goodmis.org, mingo@redhat.com, hannes@cmpxchg.org, guro@fb.com, songmuchun@bytedance.com, weixugc@google.com, gthelen@google.com Subject: Re: [RFC 1/8] mm: add overflow and underflow checks for page->_refcount Message-ID: References: <20211026173822.502506-1-pasha.tatashin@soleen.com> <20211026173822.502506-2-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211026173822.502506-2-pasha.tatashin@soleen.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 390B290000A7 X-Stat-Signature: sgkqahmh4ub97r3ubmpak5ie9u4wfmy6 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=h2scTVFQ; dmarc=none; spf=none (imf23.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-HE-Tag: 1635277840-443831 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, Oct 26, 2021 at 05:38:15PM +0000, Pasha Tatashin wrote: > static inline void page_ref_add(struct page *page, int nr) > { > - atomic_add(nr, &page->_refcount); > + int ret; > + > + VM_BUG_ON(nr <= 0); > + ret = atomic_add_return(nr, &page->_refcount); > + VM_BUG_ON_PAGE(ret <= 0, page); This isn't right. _refcount is allowed to overflow into the negatives. See page_ref_zero_or_close_to_overflow() and the conversations that led to it being added.