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 C0704C433EF for ; Tue, 14 Jun 2022 06:36:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245623AbiFNGgk (ORCPT ); Tue, 14 Jun 2022 02:36:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42160 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232644AbiFNGgf (ORCPT ); Tue, 14 Jun 2022 02:36:35 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 1CA9537BE1 for ; Mon, 13 Jun 2022 23:36:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655188592; 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=KQn/p+WJIVQNFwoaQTH0dpkpBNJBvLUauZgDvuzZ+Bc=; b=cB6lCVOm7QKlMKx1PbRPXpnKKohgwdOT5J/Ckq9vxNd5xJz4LjLMvBdYEJVDMhEm3qKqTi trSlms/UoipaD5blJ8l9+Gcj1ujEF8JD9oV9NjlZGESvFfUdcaqfDgQ4z70fYZd/Ew9lAU dGPlY85MKlzk6THVfG/56ZVG7dSWS80= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-520-nmntQT17OOOf6gW6NQ7IYQ-1; Tue, 14 Jun 2022 02:36:21 -0400 X-MC-Unique: nmntQT17OOOf6gW6NQ7IYQ-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 6B10E811E80; Tue, 14 Jun 2022 06:36:21 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.62]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6889FC28115; Tue, 14 Jun 2022 06:36:20 +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: References: To: Al Viro Cc: dhowells@redhat.com, Linus Torvalds , Dan Williams , Linux Kernel Mailing List , linux-fsdevel , nvdimm@lists.linux.dev Subject: Re: [RFC][PATCH] fix short copy handling in copy_mc_pipe_to_iter() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1586152.1655188579.1@warthog.procyon.org.uk> Date: Tue, 14 Jun 2022 07:36:19 +0100 Message-ID: <1586153.1655188579@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Al Viro wrote: > What's wrong with > p_occupancy = pipe_occupancy(head, tail); > if (p_occupancy >= pipe->max_usage) > return 0; > else > return pipe->max_usage - p_occupancy; Because "pipe->max_usage - p_occupancy" can be negative. post_one_notification() is limited by pipe->ring_size, not pipe->max_usage. The idea is to allow some slack in a watch pipe for the watch_queue code to use that userspace can't. David