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 D7F4DC00528 for ; Tue, 1 Aug 2023 14:02:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233591AbjHAOCG (ORCPT ); Tue, 1 Aug 2023 10:02:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232117AbjHAOCD (ORCPT ); Tue, 1 Aug 2023 10:02:03 -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 ESMTPS id 954181702 for ; Tue, 1 Aug 2023 07:01:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690898475; 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=7WIIC4EmcSMyslcy4PdgRwdrER+lWKYWgkhwMl2vuUk=; b=Dg+xFJgKASFidnUL4dW5Yb/xhL462nWlLhnu9x3BQQBEH4qw6uk6swMninbVJLTHkOed7S JXkxo3zGIXINmeTI36wuon9+5FXWBPoHD1Yt11jrRPE6SVxX+jfab9dTEOHKIcLnKrn/K3 Z+J3jseSqtIcFnjR6rCBfDVhSCme05g= Received: from mimecast-mx02.redhat.com (66.187.233.73 [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-696-Br2tYg1gNg20Cq9TDNc9dw-1; Tue, 01 Aug 2023 10:01:09 -0400 X-MC-Unique: Br2tYg1gNg20Cq9TDNc9dw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5EFE7299E767; Tue, 1 Aug 2023 14:01:06 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id A723240C1258; Tue, 1 Aug 2023 14:01:04 +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: <64c903b02b234_1b307829418@willemb.c.googlers.com.notmuch> References: <64c903b02b234_1b307829418@willemb.c.googlers.com.notmuch> <64c7acd57270c_169cd129420@willemb.c.googlers.com.notmuch> <64c6672f580e3_11d0042944e@willemb.c.googlers.com.notmuch> <20230718160737.52c68c73@kernel.org> <000000000000881d0606004541d1@google.com> <0000000000001416bb06004ebf53@google.com> <792238.1690667367@warthog.procyon.org.uk> <831028.1690791233@warthog.procyon.org.uk> <1401696.1690893633@warthog.procyon.org.uk> To: Willem de Bruijn Cc: dhowells@redhat.com, Jakub Kicinski , syzbot , bpf@vger.kernel.org, brauner@kernel.org, davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk Subject: Re: Endless loop in udp with MSG_SPLICE_READ - Re: [syzbot] [fs?] INFO: task hung in pipe_release (4) MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1403252.1690898464.1@warthog.procyon.org.uk> Date: Tue, 01 Aug 2023 15:01:04 +0100 Message-ID: <1403253.1690898464@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Willem de Bruijn wrote: > That getfrag is needed. For non-splice cases, to fill the linear part > of an skb. As your example shows, it is skipped if all data is covered > by pagedlen? Yes, because copy goes negative. To quote from the previously quoted log: ==>splice_to_socket() 6630 udp_sendmsg(8,8) __ip_append_data(copy=-1,len=8, mtu=8192 skblen=8189 maxfl=8188) pagedlen 9 = 9 - 0 copy -1 = 9 - 0 - 1 - 9 copy is -(the number of excess bytes). length 8 -= -1 + 0 which then gets deducted from the length - but why? I wonder if copy should be cleared if we don't call getfrag(). It looks like it's meant to deduct the amount copied by getfrag(), but that doesn't happen if copy < 0. Also, note that MSG_ZEROCOPY might see the same maths issue here. David