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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 1F985C2BA19 for ; Tue, 14 Apr 2020 16:00:03 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0A72620656 for ; Tue, 14 Apr 2020 16:00:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="UAZPoO0w" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A72620656 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=WPE2rq4Fg2K10tNh2Xj81vgbsPmx/kMLIYhE08UBQu8=; b=UAZPoO0wu1ZyWT dAU7QbyULv+zDAAkcwZHXrmfufn/DzBNN6r3hBfzVCSKyL59znwqwOT+kjKKUGuW68dhI/2GBR9IX GvhB3hhpX+dDhqqW673nRt8RZ8/Jx0fABltVu566ANDCM2fj7OWuLkXLvVtMrnU8VzhvtB97Vx5X/ 3iZGidLQvhyU90RQavQouOsS1RHDFunAYwWMFf7d+RkmdKoKXT9xXwygYVynYBTJ4mr7TdEDktnPB qJE3Q79DQn1T/0mZXKKczdFvw1CcvcLPpkEzELKCBlDJAO/ZQyk9OPJn4jmGf7hEDto08HEsP58T9 Mv0ufHN9nGE+idbQrB5g==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jONyd-0004s5-Eo; Tue, 14 Apr 2020 15:59:55 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jONyU-0004iN-3B for linux-arm-kernel@lists.infradead.org; Tue, 14 Apr 2020 15:59:51 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 83D5CC14; Tue, 14 Apr 2020 08:59:45 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AC8E83F6C4; Tue, 14 Apr 2020 08:59:44 -0700 (PDT) Date: Tue, 14 Apr 2020 16:59:42 +0100 From: Catalin Marinas To: Vincenzo Frascino Subject: Re: [PATCH 1/5] arm64: vdso: don't free unallocated pages Message-ID: <20200414155942.GC22140@gaia> References: <20200414104252.16061-1-mark.rutland@arm.com> <20200414104252.16061-2-mark.rutland@arm.com> <20200414132751.GF2486@C02TD0UTHF1T.local> <8681c958-0fd9-130e-f7bb-99bfd3a027cb@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <8681c958-0fd9-130e-f7bb-99bfd3a027cb@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200414_085946_189014_EAE4FFA0 X-CRM114-Status: GOOD ( 17.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , will@kernel.org, stable@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Apr 14, 2020 at 03:53:45PM +0100, Vincenzo Frascino wrote: > On 4/14/20 2:27 PM, Mark Rutland wrote: > > On Tue, Apr 14, 2020 at 01:50:38PM +0100, Vincenzo Frascino wrote: > >> On 4/14/20 11:42 AM, Mark Rutland wrote: > >>> The aarch32_vdso_pages[] array never has entries allocated in the C_VVAR > >>> or C_VDSO slots, and as the array is zero initialized these contain > >>> NULL. > >>> > >>> However in __aarch32_alloc_vdso_pages() when > >>> aarch32_alloc_kuser_vdso_page() fails we attempt to free the page whose > >>> struct page is at NULL, which is obviously nonsensical. > >> > >> Could you please explain why do you think that free(NULL) is "nonsensical"? > > > > Regardless of the below, can you please explain why it is sensical? I'm > > struggling to follow your argument here. > > free(NULL) is a no-operation ("no action occurs") according to the C standard > (ISO-IEC 9899 paragraph 7.20.3.2). Hence this should not cause any bug if the > allocator is correctly implemented. From what I can see the implementation of > the page allocator honors this assumption. [...] > > * page_to_virt(NULL) does not have a well-defined result, and > > page_to_virt() should only be called for a valid struct page pointer. > > The result of page_to_virt(NULL) may not be a pointer into the linear > > map as would be expected. > > Do you know why this is the case? To be compliant with what the page allocator > expects page_to_virt(NULL) should be equal to NULL. Since __free_page(page) (note the two underscores and pointer type) does not accept a NULL argument, I don't see any reason for page_to_virt() to accept NULL as a valid argument. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel