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=-6.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 176C2C433ED for ; Sun, 2 May 2021 21:16:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F14BD61284 for ; Sun, 2 May 2021 21:16:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232584AbhEBVRT (ORCPT ); Sun, 2 May 2021 17:17:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:55542 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232338AbhEBVRS (ORCPT ); Sun, 2 May 2021 17:17:18 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619990184; 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=9vKw5hk7tIYDtjcdPoLMlQVBcmuTSreBiYjqIbG38g8=; b=VZKwH3Dx4NghOOYvJyLlyauxe48Ov5cJ7pJRJ9V34cHGmH2CjZZB8nHlQzo6nnHZnB183Q noJJQlV+7gL9iwtp+Yop1d38xgFZHvOa9NbYGxyZ6TxrOaEJzZupiVhcIex0en4pgSIuOB pTP9eMMI+gLBjaYw61ETD443Tskgxvw= 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-416-RoziS3rEM7K2iJ5mKypHqQ-1; Sun, 02 May 2021 17:16:23 -0400 X-MC-Unique: RoziS3rEM7K2iJ5mKypHqQ-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 97D5F8015BA; Sun, 2 May 2021 21:16:21 +0000 (UTC) Received: from krava (unknown [10.40.192.83]) by smtp.corp.redhat.com (Postfix) with SMTP id 3F499687E4; Sun, 2 May 2021 21:16:19 +0000 (UTC) Date: Sun, 2 May 2021 23:16:18 +0200 From: Jiri Olsa To: Jiri Olsa Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , netdev@vger.kernel.org, bpf@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh Subject: Re: [PATCH RFC] bpf: Fix trampoline for functions with variable arguments Message-ID: References: <20210429212834.82621-1-jolsa@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210429212834.82621-1-jolsa@kernel.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Apr 29, 2021 at 11:28:34PM +0200, Jiri Olsa wrote: > For functions with variable arguments like: > > void set_worker_desc(const char *fmt, ...) > > the BTF data contains void argument at the end: > > [4061] FUNC_PROTO '(anon)' ret_type_id=0 vlen=2 > 'fmt' type_id=3 > '(anon)' type_id=0 > > When attaching function with this void argument the btf_distill_func_proto > will set last btf_func_model's argument with size 0 and that > will cause extra loop in save_regs/restore_regs functions and > generate trampoline code like: > > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 48 83 ec 10 sub $0x10,%rsp > 53 push %rbx > 48 89 7d f0 mov %rdi,-0x10(%rbp) > 75 f8 jne 0xffffffffa00cf007 > ^^^ extra jump > > It's causing soft lockups/crashes probably depends on what context > is the attached function called, like for set_worker_desc: > > watchdog: BUG: soft lockup - CPU#16 stuck for 22s! [kworker/u40:4:239] > CPU: 16 PID: 239 Comm: kworker/u40:4 Not tainted 5.12.0-rc4qemu+ #178 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-1.fc33 04/01/2014 > Workqueue: writeback wb_workfn > RIP: 0010:bpf_trampoline_6442464853_0+0xa/0x1000 > Code: Unable to access opcode bytes at RIP 0xffffffffa3597fe0. > RSP: 0018:ffffc90000687da8 EFLAGS: 00000217 > Call Trace: > set_worker_desc+0x5/0xb0 > wb_workfn+0x48/0x4d0 > ? psi_group_change+0x41/0x210 > ? __bpf_prog_exit+0x15/0x20 > ? bpf_trampoline_6442458903_0+0x3b/0x1000 > ? update_pasid+0x5/0x90 > ? __switch_to+0x187/0x450 > process_one_work+0x1e7/0x380 > worker_thread+0x50/0x3b0 > ? rescuer_thread+0x380/0x380 > kthread+0x11b/0x140 > ? __kthread_bind_mask+0x60/0x60 > ret_from_fork+0x22/0x30 > > This patch is removing the void argument from struct btf_func_model > in btf_distill_func_proto, but perhaps we should also check for this > in JIT's save_regs/restore_regs functions. actualy looks like we need to disable functions with variable arguments completely, because we don't know how many arguments to save I tried to disable them in pahole and it's easy fix, will post new fix jirka