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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 98907D4921F for ; Fri, 12 Dec 2025 12:18:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id ECD8E6B0005; Fri, 12 Dec 2025 07:18:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id EA5366B0006; Fri, 12 Dec 2025 07:18:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DE1C46B0007; Fri, 12 Dec 2025 07:18:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id CDCC96B0005 for ; Fri, 12 Dec 2025 07:18:22 -0500 (EST) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 7E57712F6CD for ; Fri, 12 Dec 2025 12:18:22 +0000 (UTC) X-FDA: 84210721644.16.6CE1A4E Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf04.hostedemail.com (Postfix) with ESMTP id 74D9440012 for ; Fri, 12 Dec 2025 12:18:20 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=cfKnlzfV; dmarc=pass (policy=none) header.from=infradead.org; spf=none (imf04.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=1765541901; a=rsa-sha256; cv=none; b=W6mZbi5Fa+vDHGA46BQqgJbbtVOtPjcz8ZrWf7tr5j3jHd/R0bYrsfmtUfnSb03Xck0RUT Adv6fGxj/Hv+7KfTbXKKvBJlxymtora5u5HHwygdnjAOsMFAqMC0IVv+nDae6ZvJVb42Jh CwWm57Xmh3n7NMiKv+QU6LNXN1gvSqk= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=cfKnlzfV; dmarc=pass (policy=none) header.from=infradead.org; spf=none (imf04.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=1765541901; 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=w4e7B+E8LkBy1p188ZJwv5Wln/swonn5oRIyMMDWppE=; b=3Er60qtnC7gobxCC9S/0lhK7JR7vP0aj45ZLaXYyu/lFgVPgRHiR5tWBKzRs6ZKwyG8peL /hbhCRL6sCQ81eAjCEhinJAIFXOTQho0/0cGwGCvwLOYmr7js0FGAw4WnYAQ5JCKwIDCMS Zqaf2H6UZt0DDcRg/qSCGGKcECeUmX4= 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=w4e7B+E8LkBy1p188ZJwv5Wln/swonn5oRIyMMDWppE=; b=cfKnlzfV9QrsH5hMOhmPUAJhXy XjEPNpRNJpEyUWUD58b2u3CldeYoF3Yxr90xzhUkPWmFS1Icv8hUVhfORCvWwE7UHE+RlwbWt7xVO vUeggPll8nmxfPGQsbuyfrPGqVqU41vL0lNYf7j8jUjLggJ8BRxZWITJ3vVe51BDVUW0hqkQupPc+ f7WZx7HJjp4C3PcTjQnbWyuhUOFOYenRuQWMtitcijzVGhxR915iboxfs7Ee1vZy32cOADi1nX5gw D3x1yPOOSDbg/a0QcNlh5HrUrMb5n1ze3FR3M6LvMSEFYshjNaC35qw1f9xyIoqiBFvyMG1c8MC0u uyKZfm9A==; Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vU267-0000000FfEK-2ukU; Fri, 12 Dec 2025 12:18:11 +0000 Date: Fri, 12 Dec 2025 12:18:11 +0000 From: Matthew Wilcox To: Jan Kara Cc: Deepakkumar Karn , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Liam.Howlett@oracle.com, Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] pagemap: Add alert to mapping_set_release_always() for mapping with no release_folio Message-ID: References: <20251210200104.262523-1-dkarn@redhat.com> <5edukhcwwr6foo67isfum3az6ds6tcmgrifgthwtivho6ffjmw@qrxmadbaib3l> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5edukhcwwr6foo67isfum3az6ds6tcmgrifgthwtivho6ffjmw@qrxmadbaib3l> X-Rspam-User: X-Rspamd-Queue-Id: 74D9440012 X-Rspamd-Server: rspam10 X-Stat-Signature: 8u45z9bo48zb8nqx533967s7czq5zxwy X-HE-Tag: 1765541900-804373 X-HE-Meta: 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 NZ90WA7n 7xn+C 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: List-Subscribe: List-Unsubscribe: On Thu, Dec 11, 2025 at 10:23:13AM +0100, Jan Kara wrote: > On Wed 10-12-25 21:36:43, Matthew Wilcox wrote: > > On Thu, Dec 11, 2025 at 01:31:04AM +0530, Deepakkumar Karn wrote: > > > static inline void mapping_set_release_always(struct address_space *mapping) > > > { > > > + /* Alert while setting the flag with no release_folio callback */ > > > > The comment is superfluous. > > Agreed. > > > > + VM_WARN_ONCE(!mapping->a_ops->release_folio, > > > + "Setting AS_RELEASE_ALWAYS with no release_folio"); > > > > But you haven't said why we need to do this. Surely the NULL pointer > > splat is enough to tell you that you did something stupid? > > Well, but this will tell it much earlier and it will directly point to the > place were you've done the mistake (instead of having to figure out why > drop_buffers() is crashing on you). So I think this assert makes sense to > ease debugging and as kind of self-reminding documentation :). Oh. So the real problem here is this: if (mapping && mapping->a_ops->release_folio) return mapping->a_ops->release_folio(folio, gfp); return try_to_free_buffers(folio); We should have a block_release_folio(), change all the BH-based filesystems to add it to their aops, and then change filemap_release_folio() to do: if (mapping) return mapping->a_ops->release_folio(folio, gfp); return true; (actually, can the !mapping case be hit? surely this can't be called for folios which have already been truncated?) Then you get a nice NULL pointer dereference instead of calling into try_to_free_buffers() which is as confusing as hell.