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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2438C46467 for ; Tue, 3 Jan 2023 15:32:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 273D48E0003; Tue, 3 Jan 2023 10:32:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2233D8E0001; Tue, 3 Jan 2023 10:32:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 113768E0003; Tue, 3 Jan 2023 10:32:03 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id F2C5E8E0001 for ; Tue, 3 Jan 2023 10:32:02 -0500 (EST) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 7713DAAEEB for ; Tue, 3 Jan 2023 15:32:02 +0000 (UTC) X-FDA: 80313878484.15.51327B9 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf26.hostedemail.com (Postfix) with ESMTP id 67269140013 for ; Tue, 3 Jan 2023 15:31:59 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=e5jv2AL9; dmarc=none; spf=none (imf26.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1672759920; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=tYB2JZE2N0WqTPWcsY2cJZJix0I7cJCxTxV5O4mNf00=; b=c2TM8Ac23SD2PIWJ+tP1oslpuMR9ZNO3m7B0H9nmPRGGLJJA26KtmlwVclIiCbxy3BZ0E3 Ui0tDTzcdV89k4vJBEpdwbEoPDhr1zsYMaSrW3xxhUuTkYQW1qCv6w72ynCEveWUYFgCfP iXOqhlmPvWR7JwJuLMyW5/iya3/U/SM= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=e5jv2AL9; dmarc=none; spf=none (imf26.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1672759920; a=rsa-sha256; cv=none; b=ZbuqxB5fR6T3L4UG6hx7Go6xt4H+dQcUuN/8HD4zUKKAka/GKWbM5uzb8LLvvaaH0iYO7L 4gOX3qZKIrOOG8/NMey4tkE6YCX13awrsc6UTvsHUjc3TEELbO1HlOWmtLKLSds/rqk2nm GxEjvG1ycljgTXNWk2/gVE9RA9wkCpU= 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=tYB2JZE2N0WqTPWcsY2cJZJix0I7cJCxTxV5O4mNf00=; b=e5jv2AL9yGM5fFtgcVIjLQBfU6 9nI7bN3KEFRKBs7n+Q+yhCiQIpbuSUEiSWczKzLuui2JWaq0xcmVGJ9UfeEj2tZOrL1BCDp8LBVih /iYkhtP0eJJYwY5R1H63IErkwXLJcZejtyrM9PbgSSjiDkMqwBr/fyovTXH0Zbd3ssmeCRgAJ5hBZ TqlR1LsNWUgE0V25W7RDR1KvZIKR9PLTXMT3EM3nyECFk4nL30HO0utjok8Fn0vfVKangD21FRlVp xdTELx4xqcPxigyfX56kBGZ+rS2fR32CZIT/p7FZb4tvtUbgG3h5iiWzxLQzQqPvGBUSs/6mnOQ+9 AINeyHEg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pCjGR-00EDwR-3V; Tue, 03 Jan 2023 15:31:43 +0000 Date: Tue, 3 Jan 2023 15:31:43 +0000 From: Matthew Wilcox To: Vlastimil Babka Cc: kernel test robot , Hyeonggon Yoo <42.hyeyoo@gmail.com>, oe-lkp@lists.linux.dev, lkp@intel.com, Mike Rapoport , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: A better dump_page() Message-ID: References: <202212312021.bc1efe86-oliver.sang@intel.com> <41276905-b8a5-76ae-8a17-a8ec6558e988@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41276905-b8a5-76ae-8a17-a8ec6558e988@suse.cz> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 67269140013 X-Stat-Signature: 7op75yu769skg1o7oqi98b7c834a749f X-HE-Tag: 1672759919-272695 X-HE-Meta: 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 4vQ== 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, Jan 03, 2023 at 11:42:11AM +0100, Vlastimil Babka wrote: > Separately we should also make the __dump_page() more resilient. Right. It's not ideal when one of our best debugging tools obfuscates the problem we're trying to debug. I've seen probems like this before, and the problem is that somebody calls dump_page() on a page that they don't own a refcount on. That lets the page mutate under us in some fairly awkward ways (as you've seen here, it seems to be part of several different compound allocations at various points during the dump process). One possibility I thought about was taking our own refcount on the page at the start of dump_page(). That would kill off the possibility of ever passing in a const struct page, and it would confuse people. Also, what if somebody passes in a pointer to something that's not a struct page? Then we've (tried to) modify memory that's not a refcount. I think the best we can do is to snapshot the struct page and the folio it appears to belong to at the start of dump_page(). It'll take a little care (for example, folio_pfn() must be passed the original folio, and not the snapshot), but I think it's doable.