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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B76A1EB64D7 for ; Fri, 16 Jun 2023 22:43:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229482AbjFPWnw (ORCPT ); Fri, 16 Jun 2023 18:43:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36394 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229696AbjFPWnu (ORCPT ); Fri, 16 Jun 2023 18:43:50 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 57012359D for ; Fri, 16 Jun 2023 15:43:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686955388; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xil8pYQHFvvvTl9T7ZZLQkZeu1j0WF7ytBjn1P1WCeA=; b=VpqtiYrkk1WEwApRkU5EzodIPxzuJfyMBTADhkJn6jAOBY/XCuFa1tyWeo+GoCu1W+rVYT N47WizLdlwk+CukPhl+edETOG9b8k3QkhT4gjMnxATmbbLqvKBJoSq+ZAEFrghjWb0FXc1 ptRre7vfQ+OHlFVzURAvU8k9PdiVD+o= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-607-zpiW6TjfOayuMdK63qkmJg-1; Fri, 16 Jun 2023 18:43:05 -0400 X-MC-Unique: zpiW6TjfOayuMdK63qkmJg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 166873855576; Fri, 16 Jun 2023 22:43:04 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.51]) by smtp.corp.redhat.com (Postfix) with ESMTP id 77724C1603B; Fri, 16 Jun 2023 22:43:03 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20230608175031.9c534e7f554de89e3d972ab2@linux-foundation.org> References: <20230608175031.9c534e7f554de89e3d972ab2@linux-foundation.org> <20230607204120.89416-1-vishal.moola@gmail.com> <20230607204120.89416-2-vishal.moola@gmail.com> To: Andrew Morton Cc: dhowells@redhat.com, "Vishal Moola (Oracle)" , linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] afs: Fix waiting for writeback then skipping folio MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <702178.1686955382.1@warthog.procyon.org.uk> Date: Fri, 16 Jun 2023 23:43:02 +0100 Message-ID: <702179.1686955382@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > > Commit acc8d8588cb7 converted afs_writepages_region() to write back a > > folio batch. The function waits for writeback to a folio, but then > > proceeds to the rest of the batch without trying to write that folio > > again. This patch fixes has it attempt to write the folio again. > > > > This has only been compile tested. > > This seems fairly serious? We will try to write the again later, but sync()/fsync() might now have skipped it. > From my reading, we'll fail to write out the dirty data. Presumably > not easily observable, as it will get written out again later on. As it's a network filesystem, interactions with third parties could cause apparent corruption. Closing a file will flush it - but if there's a simultaneous op of some other kind, a bit of a flush or a sync may get missed and the copy visible to another user be temporarily missing that bit. > But we're also calling afs_write_back_from_locked_folio() with an unlocked > folio, which might cause mayhem. Without this patch, you mean? There's a "continue" statement that should send us back to the top of the loop before we get as far as afs_write_back_from_locked_folio() - and then the folio_unlock() there would go bang. David