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 X-Spam-Level: X-Spam-Status: No, score=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B03DC433F5 for ; Thu, 16 Sep 2021 15:30:29 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E5C1A61246 for ; Thu, 16 Sep 2021 15:30:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E5C1A61246 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631806228; h=from:from:sender: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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=U4QIK3gSULfMZT716J8dvNps2rlI32MFS1hiSVfZbuo=; b=Pe/J9/UXbe6flzPIX+CstLPrjv6qzHgj/K4YLNWnoecOWcspHdjW3UQoZMww31qaLIGvUc 5LS5LDU6xT7anBGVmkuvC7bNyIxDFKMwBEx5JIxds4nLbQNvq90c+SI/jkRUhfHi9k/IPI Hn83QRV6dKP454UATAbGlKEbccUq4Io= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-535-Qk3ovgjgMKSiwMN24112cQ-1; Thu, 16 Sep 2021 11:30:26 -0400 X-MC-Unique: Qk3ovgjgMKSiwMN24112cQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 943D810144F3; Thu, 16 Sep 2021 15:30:21 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5374B83C0D; Thu, 16 Sep 2021 15:30:21 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id BC4B61800FE4; Thu, 16 Sep 2021 15:30:20 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 18GFQgHv030449 for ; Thu, 16 Sep 2021 11:26:42 -0400 Received: by smtp.corp.redhat.com (Postfix) id C19131045E0A; Thu, 16 Sep 2021 15:26:42 +0000 (UTC) Received: from octiron.msp.redhat.com (unknown [10.15.80.209]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BA6F81017CE8; Thu, 16 Sep 2021 15:26:25 +0000 (UTC) Received: from octiron.msp.redhat.com (localhost.localdomain [127.0.0.1]) by octiron.msp.redhat.com (8.14.9/8.14.9) with ESMTP id 18GFQNmU012118; Thu, 16 Sep 2021 10:26:23 -0500 Received: (from bmarzins@localhost) by octiron.msp.redhat.com (8.14.9/8.14.9/Submit) id 18GFQMdZ012117; Thu, 16 Sep 2021 10:26:22 -0500 Date: Thu, 16 Sep 2021 10:26:21 -0500 From: Benjamin Marzinski To: Martin Wilck Message-ID: <20210916152621.GZ3087@octiron.msp.redhat.com> References: <20210910114120.13665-1-mwilck@suse.com> <20210910114120.13665-34-mwilck@suse.com> <20210916042253.GS3087@octiron.msp.redhat.com> <3729ec7dc41fe81c9db8d2c553c5ccc2cdb3d496.camel@suse.com> MIME-Version: 1.0 In-Reply-To: <3729ec7dc41fe81c9db8d2c553c5ccc2cdb3d496.camel@suse.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-loop: dm-devel@redhat.com Cc: lixiaokeng@huawei.com, dm-devel@redhat.com, Chongyun Wu Subject: Re: [dm-devel] [PATCH 33/35] multipathd: uxlsnr: use poll loop for sending, too X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable On Thu, Sep 16, 2021 at 11:33:29AM +0200, Martin Wilck wrote: > On Wed, 2021-09-15 at 23:22 -0500, Benjamin Marzinski wrote: > > On Fri, Sep 10, 2021 at 01:41:18PM +0200, mwilck@suse.com=A0wrote: > > > From: Martin Wilck > > >=20 > > > send_packet() may busy-loop. By polling for POLLOUT, we can > > > avoid that, even if it's very unlikely in practice. > > >=20 > > > Signed-off-by: Martin Wilck > > > --- > > > =A0multipathd/uxlsnr.c | 39 ++++++++++++++++++++++++++++++++------- > > > =A01 file changed, 32 insertions(+), 7 deletions(-) > > >=20 > > > diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c > > > index 1bf4126..c18b2c4 100644 > > > --- a/multipathd/uxlsnr.c > > > +++ b/multipathd/uxlsnr.c > > > @@ -588,15 +588,37 @@ static void handle_client(struct client *c, > > > struct vectors *vecs, short revents) > > > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (get_strbuf_len(&c= ->reply) =3D=3D 0) > > > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0default_reply(c, c->error); > > > =A0 > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0const char *buf =3D get= _strbuf_str(&c->reply); > > > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (c->cmd_len =3D=3D 0= ) { > > > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0size_t len =3D get_strbuf_len(&c->reply) + 1; > > > =A0 > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (send_packet(c->fd, = buf) !=3D 0) > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0dead_client(c); > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0else > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0condlog(4, "cli[%d]: Reply [%zu bytes]", c- > > > >fd, > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0get_strbuf_len(&c->reply) + 1); > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0reset_strbuf(&c->reply)= ; > > > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0if (send(c->fd, &len, sizeof(len), > > > MSG_NOSIGNAL) > > > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0 !=3D sizeof(len)) { > >=20 > > This assumes that failing to send the size is always an error. What > > about if we get EINTR/EAGAIN? Also, it seems pretty likely that we will > > either send all of the size or none of it, but I'm not sure we can > > guarantee that.=A0 send_packet() handled partitial writes of the length= . > > Actually, mpath_recv_reply_len() which is still used by CLT_RECV still > > uses read_all(), instead of just polling again on partial reads. >=20 > That was intentional. I couldn't imagine that reading or writing 8 > bytes would block (after all, we received POLLIN / POLLOUT for the > socket). Note the minimum socket buffer size that the kernel uses=A0is > larger than 2048 bytes. >=20 > https://elixir.bootlin.com/linux/latest/source/include/net/sock.h#L2339 >=20 > When we send the size value, the send buffer is empty by definition > (even for interactive sessions, if the client uses libmpathcmd, it will > have fetched the response before sending new requests). Likewise for > receiving, the size will be received in one piece if the client uses > libmpathcmd. >=20 > I take it that some malicious or badly designed client could access the > socket bypassing libmpathcmd, sending or receiving the size byte-by- > byte, or in other strange patterns. But I think we are within our > rights to error out in such cases; it may actually be the right thing > to do that, as we don't really want to service clients doing tricks > like that. I will do some tests. In this case, calling mpath_recv_reply_len() is probably overkill. =20 > > Also, the fd is not set to be non-blocking. and if we fall through to > > CLT_SEND, we haven't checked for a POLLOUT revent, so technically, I > > believe the write could block here. >=20 > Right, we have to do that. Thanks for pointing it out. This also means > that polling in read_all() and send_packet() was pointless in the first > place ... >=20 > Thanks! > Martin >=20 > PS: I was wondering why we haven't been using SOCK_DGRAM for the > multipath socket in the first place. It would have avoided all this > hassle... That design decision predates me working on the code. -Ben >=20 -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel