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 C32C9C0015E for ; Tue, 25 Jul 2023 12:52:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DD5926B0071; Tue, 25 Jul 2023 08:52:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D85686B0074; Tue, 25 Jul 2023 08:52:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C4D4D6B0075; Tue, 25 Jul 2023 08:52:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id B5EAE6B0071 for ; Tue, 25 Jul 2023 08:52:36 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 85A2540E2A for ; Tue, 25 Jul 2023 12:52:36 +0000 (UTC) X-FDA: 81050123112.02.A69A1FB Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf19.hostedemail.com (Postfix) with ESMTP id 203141A0003 for ; Tue, 25 Jul 2023 12:52:33 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=UgAJBFRL; spf=none (imf19.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1690289554; a=rsa-sha256; cv=none; b=C+I/v4c3g8WouGhJYaNMGcdyVhTiwnCBpKc3SqLxj7or9Kfd5dyXzVDXCX85eF3lnAPjXX XV871FtMEB/KBzNsYVTFXomDA7eHnvDtvC5ExaPro3Av/WXC7kh015NbQuZvfOP6AMSCqe xnQ0qgrGFEgmDb+LkykzadzFJUvNYk4= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=UgAJBFRL; spf=none (imf19.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1690289554; 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=cip1L4+WNN72lEdlEtgKKz6+Th/GNW6kyU+RnxFbZZ8=; b=YZ12yeqOYyfLLqtuwDFx9QfL/XHCmKXnLj2cUEnQbA1l/sld/auuor68YA4+hnbqQr9ICZ zahPoPfXURjNaKhmR/OLLHPaHpdbWT/GU2uUqKsll3dKKB5XedItAM3mBr+OCw3FmTVHdT zXcUrHBLPDsExb7tJ80KWnjyga8Rqu8= 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=cip1L4+WNN72lEdlEtgKKz6+Th/GNW6kyU+RnxFbZZ8=; b=UgAJBFRLO20d1Q4UeecSqlBQIs PFHuz0NUmB/1Y+2cEVFvwqnHb1BSxWW4RhQ2P8kvsu3ACbwOqr57viJKTa7uG+qe1fdufl5rqF2qr jHy5L3HlBpbKr1Vl5EefvCAyn8+oe9n/K+eN0UUCvHZ3OgwtPhyspcNh4yAoE49KOIUkQVp2v0HR9 +xKnn/gm3dSYH0IDK2KkKvdpo4YPQW6CLliHGifFEImfRxrevzUzbI0xJBT7SCfU6e7LIrXsQ1mlT uc0IdyK39Z/Ut2VF+t8tpW9pm9g50y0Q3SwS/URKZyTPqyVYvUikuYgn7PDUb1oSxM38pOnLhiEyt M5/wJdyg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qOHW7-005Tcv-AA; Tue, 25 Jul 2023 12:51:55 +0000 Date: Tue, 25 Jul 2023 13:51:55 +0100 From: Matthew Wilcox To: "Kirill A . Shutemov" Cc: Sean Christopherson , Vlastimil Babka , Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Andrew Morton , Paul Moore , James Morris , "Serge E. Hallyn" , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Chao Peng , Fuad Tabba , Jarkko Sakkinen , Yu Zhang , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata Subject: Re: [RFC PATCH v11 10/29] mm: Add AS_UNMOVABLE to mark mapping as completely unmovable Message-ID: References: <20230718234512.1690985-1-seanjc@google.com> <20230718234512.1690985-11-seanjc@google.com> <20230725102403.xywjqlhyqkrzjok6@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230725102403.xywjqlhyqkrzjok6@box.shutemov.name> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 203141A0003 X-Stat-Signature: dsgt5pwcsoaux6rxnsotrk1fzczc7n1k X-Rspam-User: X-HE-Tag: 1690289553-19737 X-HE-Meta: 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 GaYOW+Ye CT8mVKgTFhfMZG8ZP8TYIJU2R1GkESXs51thT0+zcn73+J9fvatAJDMXsU3qnN5WzaqXGeW/s+UQ2sHUJ3PbqG+FwFKXUypXUjViuGtnf2QFrb8Vkpb/8PwBgU3CtwWfiaFHnh5yLslyC4cBo4rzy4EgRiL55Rr3WksnKKI4efh7jGwD/eABTyVbGtT4isOIqFiP7fnlcmIyr+t4rq8PAQGICWqTrl2fKbmSUJF1TJv3lIoMLmOkRe6ekkiHS7NINvK4L 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, Jul 25, 2023 at 01:24:03PM +0300, Kirill A . Shutemov wrote: > On Tue, Jul 18, 2023 at 04:44:53PM -0700, Sean Christopherson wrote: > > diff --git a/mm/compaction.c b/mm/compaction.c > > index dbc9f86b1934..a3d2b132df52 100644 > > --- a/mm/compaction.c > > +++ b/mm/compaction.c > > @@ -1047,6 +1047,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > if (!mapping && (folio_ref_count(folio) - 1) > folio_mapcount(folio)) > > goto isolate_fail_put; > > > > + /* The mapping truly isn't movable. */ > > + if (mapping && mapping_unmovable(mapping)) > > + goto isolate_fail_put; > > + > > I doubt that it is safe to dereference mapping here. I believe the folio > can be truncated from under us and the mapping freed with the inode. > > The folio has to be locked to dereference mapping safely (given that the > mapping is still tied to the folio). There's even a comment to that effect later on in the function: /* * Only pages without mappings or that have a * ->migrate_folio callback are possible to migrate * without blocking. However, we can be racing with * truncation so it's necessary to lock the page * to stabilise the mapping as truncation holds * the page lock until after the page is removed * from the page cache. */ (that could be reworded to make it clear how dangerous dereferencing ->mapping is without the lock ... and it does need to be changed to say "folio lock" instead of "page lock", so ...) How does this look? /* * Only folios without mappings or that have * a ->migrate_folio callback are possible to * migrate without blocking. However, we can * be racing with truncation, which can free * the mapping. Truncation holds the folio lock * until after the folio is removed from the page * cache so holding it ourselves is sufficient. */