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=-16.0 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 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 9D0CDC433C1 for ; Tue, 23 Mar 2021 21:00:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 772C3619A5 for ; Tue, 23 Mar 2021 21:00:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233477AbhCWVAX (ORCPT ); Tue, 23 Mar 2021 17:00:23 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:39511 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233466AbhCWU74 (ORCPT ); Tue, 23 Mar 2021 16:59:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616533196; 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=nEJEAGnBDrkMwTac8x1suOx88OEJOU7HbYOYLwosHvY=; b=LuYrEdP26loRRr5HeFSuB+Hd2f0DM8t+CggHgGpkQOebVzTMVr06W25h6PH89qjYcd5pJA 3j/8TrWTtru5CykfE+Oeiq+ywpkR+NewRQZDSOfnTe6cCRorVkZg2nQ6vnsifjS5oBlDhZ pweRVonhtvJD5yR4Ko7ZsrWoZ4yjpfE= 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-366-00Yh_wfXMpa44y5FFklzFA-1; Tue, 23 Mar 2021 16:59:51 -0400 X-MC-Unique: 00Yh_wfXMpa44y5FFklzFA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 027AD100746C; Tue, 23 Mar 2021 20:59:50 +0000 (UTC) Received: from krava (unknown [10.40.192.135]) by smtp.corp.redhat.com (Postfix) with SMTP id A39DD5C1CF; Tue, 23 Mar 2021 20:59:47 +0000 (UTC) Date: Tue, 23 Mar 2021 21:59:46 +0100 From: Jiri Olsa To: Alexei Starovoitov Cc: Steven Rostedt , Alexei Starovoitov , davem@davemloft.net, daniel@iogearbox.net, andrii@kernel.org, paulmck@kernel.org, bpf@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH bpf] bpf: Fix fexit trampoline. Message-ID: References: <20210316210007.38949-1-alexei.starovoitov@gmail.com> <20210323085900.3bdc0002@gandalf.local.home> <6d8ad633-b464-0a72-a310-2dda27dfeb99@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6d8ad633-b464-0a72-a310-2dda27dfeb99@fb.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Mar 23, 2021 at 07:50:55AM -0700, Alexei Starovoitov wrote: > On 3/23/21 5:59 AM, Steven Rostedt wrote: > > On Mon, 22 Mar 2021 19:53:10 +0100 > > Jiri Olsa wrote: > > > > > On Mon, Mar 22, 2021 at 05:24:26PM +0100, Jiri Olsa wrote: > > > > On Mon, Mar 22, 2021 at 12:32:05AM +0100, Jiri Olsa wrote: > > > > > On Tue, Mar 16, 2021 at 02:00:07PM -0700, Alexei Starovoitov wrote: > > > > > > From: Alexei Starovoitov > > > > > > > > > > > > The fexit/fmod_ret programs can be attached to kernel functions that can sleep. > > > > > > The synchronize_rcu_tasks() will not wait for such tasks to complete. > > > > > > In such case the trampoline image will be freed and when the task > > > > > > wakes up the return IP will point to freed memory causing the crash. > > > > > > Solve this by adding percpu_ref_get/put for the duration of trampoline > > > > > > and separate trampoline vs its image life times. > > > > > > The "half page" optimization has to be removed, since > > > > > > first_half->second_half->first_half transition cannot be guaranteed to > > > > > > complete in deterministic time. Every trampoline update becomes a new image. > > > > > > The image with fmod_ret or fexit progs will be freed via percpu_ref_kill and > > > > > > call_rcu_tasks. Together they will wait for the original function and > > > > > > trampoline asm to complete. The trampoline is patched from nop to jmp to skip > > > > > > fexit progs. They are freed independently from the trampoline. The image with > > > > > > fentry progs only will be freed via call_rcu_tasks_trace+call_rcu_tasks which > > > > > > will wait for both sleepable and non-sleepable progs to complete. > > > > > > > > > > > > Reported-by: Andrii Nakryiko > > > > > > Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline") > > > > > > Signed-off-by: Alexei Starovoitov > > > > > > Acked-by: Paul E. McKenney # for RCU > > > > > > --- > > > > > > Without ftrace fix: > > > > > > https://patchwork.kernel.org/project/netdevbpf/patch/20210316195815.34714-1-alexei.starovoitov@gmail.com/ > > > > > > this patch will trigger warn in ftrace. > > > > > > > > > > > > arch/x86/net/bpf_jit_comp.c | 26 ++++- > > > > > > include/linux/bpf.h | 24 +++- > > > > > > kernel/bpf/bpf_struct_ops.c | 2 +- > > > > > > kernel/bpf/core.c | 4 +- > > > > > > kernel/bpf/trampoline.c | 218 +++++++++++++++++++++++++++--------- > > > > > > 5 files changed, 213 insertions(+), 61 deletions(-) > > > > > > > > > > hi, > > > > > I'm on bpf/master and I'm triggering warnings below when running together: > > > > > > > > > > # while :; do ./test_progs -t fentry_test ; done > > > > > # while :; do ./test_progs -t module_attach ; done > > > > > > > > hum, is it possible that we don't take module ref and it can get > > > > unloaded even if there's trampoline attach to it..? I can't see > > > > that in the code.. ftrace_release_mod can't fail ;-) > > > > > > when I get the module for each module trampoline, > > > I can no longer see those warnings (link for Steven): > > > https://lore.kernel.org/bpf/YFfXcqnksPsSe0Bv@krava/ > > > > > > Steven, > > > I might be missing something, but it looks like module > > > can be unloaded even if the trampoline (direct function) > > > is registered in it.. is that right? > > > > > > > Not with your patch below ;-) > > > > But yes, ftrace does not currently manage module text for direct calls, > > it's assumed that whoever attaches to the module text would do that. But > > I'm not adverse to the patch below. > > Jiri, > > could you please refactor your patch to do the same in bpf trampoline? right, we need to take care about bpf_arch_text_poke interface as well.. I'll resend > The selftest/bpf would be great as well. It can come as a follow up. > Let's fix the issue for bpf tree first. ok, will send test later jirka