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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0B6B0E7B5EE for ; Wed, 4 Oct 2023 11:12:22 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qnznW-0000qV-8a; Wed, 04 Oct 2023 07:12:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qnznT-0000pi-Os for qemu-devel@nongnu.org; Wed, 04 Oct 2023 07:12:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qnznR-0004uj-U5 for qemu-devel@nongnu.org; Wed, 04 Oct 2023 07:12:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1696417925; 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=3naIuioo+PaO17QwTvZI64uG0HSvqOxEkNNyw/Nqxw4=; b=NmdGL2ySxTvsNW+4VwtBs+Bkpo7pJs+NW3Lvltw37Tc3uq4jw4QwfSVh768yT0b2iaguow hCbpGFCWcXSv6vJmvRCbYcZ+R9KphvmfR1gRC9y1oDjWrpWbc3+sJJpoTaeZ2fjbJ4+J7k vsnMvaMa03GXpLa3E8x4T4mtvwLNj+A= Received: from mimecast-mx02.redhat.com (mx-ext.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-300-GhJmxOKBMuecG9sqbDejUw-1; Wed, 04 Oct 2023 07:12:01 -0400 X-MC-Unique: GhJmxOKBMuecG9sqbDejUw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 740131C05AA9; Wed, 4 Oct 2023 11:12:01 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 47B7F40C6EA8; Wed, 4 Oct 2023 11:12:01 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 37C2721E6904; Wed, 4 Oct 2023 13:12:00 +0200 (CEST) From: Markus Armbruster To: Fabiano Rosas Cc: qemu-devel@nongnu.org, quintela@redhat.com, peterx@redhat.com, leobras@redhat.com, lizhijian@fujitsu.com, eblake@redhat.com Subject: Re: [PATCH v2 16/53] migration/rdma: Fix or document problematic uses of errno References: <20230928132019.2544702-1-armbru@redhat.com> <20230928132019.2544702-17-armbru@redhat.com> <87y1gpyq24.fsf@suse.de> Date: Wed, 04 Oct 2023 13:12:00 +0200 In-Reply-To: <87y1gpyq24.fsf@suse.de> (Fabiano Rosas's message of "Fri, 29 Sep 2023 12:09:07 -0300") Message-ID: <875y3miqv3.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Fabiano Rosas writes: > Markus Armbruster writes: > >> We use errno after calling Libibverbs functions that are not >> documented to set errno (manual page does not mention errno), or where >> the documentation is unclear ("returns [...] the value of errno on >> failure"). While this could be read as "sets errno and returns it", >> a glance at the source code[*] kills that hope: >> >> static inline int ibv_post_send(struct ibv_qp *qp, struct ibv_send_wr *wr, >> struct ibv_send_wr **bad_wr) >> { >> return qp->context->ops.post_send(qp, wr, bad_wr); >> } >> >> The callback can be >> >> static int mana_post_send(struct ibv_qp *ibqp, struct ibv_send_wr *wr, >> struct ibv_send_wr **bad) >> { >> /* This version of driver supports RAW QP only. >> * Posting WR is done directly in the application. >> */ >> return EOPNOTSUPP; >> } >> >> Neither of them touches errno. >> >> One of these errno uses is easy to fix, so do that now. Several more >> will go away later in the series; add temporary FIXME commments. >> Three will remain; add TODO comments. TODO, not FIXME, because the >> bug might be in Libibverbs documentation. >> >> [*] https://github.com/linux-rdma/rdma-core.git >> commit 55fa316b4b18f258d8ac1ceb4aa5a7a35b094dcf >> >> Signed-off-by: Markus Armbruster >> --- >> migration/rdma.c | 45 +++++++++++++++++++++++++++++++++++++++------ >> 1 file changed, 39 insertions(+), 6 deletions(-) >> >> diff --git a/migration/rdma.c b/migration/rdma.c >> index 28097ce604..bba8c99fa9 100644 >> --- a/migration/rdma.c >> +++ b/migration/rdma.c >> @@ -853,6 +853,12 @@ static int qemu_rdma_broken_ipv6_kernel(struct ibv_context *verbs, Error **errp) >> >> for (x = 0; x < num_devices; x++) { >> verbs = ibv_open_device(dev_list[x]); >> + /* >> + * ibv_open_device() is not documented to set errno. If >> + * it does, it's somebody else's doc bug. If it doesn't, >> + * the use of errno below is wrong. >> + * TODO Find out whether ibv_open_device() sets errno. >> + */ >> if (!verbs) { >> if (errno == EPERM) { >> continue; > > This function can call into glibc, so it's not unreasonable to expect > errno to be set at some point. We're not relying on errno to be set, > just taking an action if it happens to be. errno may well be set on some failures. But it needs to be set on *all* failures to be reliable. If it's not, then its value on such failures comes from some unrelated, prior errno-setting failure. > I don't think someone would just decide to handle EPERM at this point > for no reason. Specially since the manual makes no mention to > errno. This was probably introduced after someone got bit by it. > > ... indeed the commit 5b61d57521 ("rdma: Fix qemu crash when IPv6 > address is used for migration") introduced this to fix a crash. I don't doubt the error recovery added there works in the case described by the commit message. I suspect it can break on unrelated failures.