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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3BBFAC433EF for ; Tue, 19 Oct 2021 13:19:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12D8F610E7 for ; Tue, 19 Oct 2021 13:19:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231564AbhJSNWF (ORCPT ); Tue, 19 Oct 2021 09:22:05 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49871 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230267AbhJSNWF (ORCPT ); Tue, 19 Oct 2021 09:22:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634649592; 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=AyjIVFec2gOJzFffy5THbXxA66XevsHzKt+shtTsAk4=; b=OmTh80PSlgGblz+ks9yOMXChLJIsu4ExLxNwexdBMpow2ct9jaD65tg/RIUYsssF44iXll Z9mx6Ztfvyn4PyY2oBoylGpEB8D46u7vZsLkFKEu2LvLFFBDJtwN0RcU5xldWp6+Tfwh8F mv8EFACEQKWBGl9nIhO66/MqtyiiQvs= Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-556-UmcDsy76OE67c8cBrh4RoA-1; Tue, 19 Oct 2021 09:19:50 -0400 X-MC-Unique: UmcDsy76OE67c8cBrh4RoA-1 Received: by mail-ed1-f70.google.com with SMTP id c30-20020a50f61e000000b003daf3955d5aso17585215edn.4 for ; Tue, 19 Oct 2021 06:19:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=AyjIVFec2gOJzFffy5THbXxA66XevsHzKt+shtTsAk4=; b=lBw1TX6nL5XAhTtCz0zrjP1U9UOvwkIODn1JbZkM63D1o5Km7BapjqZ6lNsl2LADEj M4e54lk5Q4FXUy7J0x+R74X5iEJ6SpPgZX2u5D20XV8Q7J6eb5GxqyUG9q0qKMzCOJDd /A3Rgi921Wl8wgE6V7Q8wwsCzpOQnou9GweNBVHesYGnXtM00oiCJGAYjCsfVKJ636ao 6NoOwywnKMQKYCvgvBN2NXs7Ap5t71ksSIln82aDWpY80Voy+7kY34TjZ0DR8qK1sSwn Gxzsqm0/kFYIhXkrojV2kYeg5EAbrEpJ/2Eq9qYN9y+hRwL6bdLcbGmFQ7f79eYw/1j9 0pGg== X-Gm-Message-State: AOAM5310rUqIBVJ7lqOcADfO0Ky+XBnX0eiL8klEMJEnrQz3two6dtPB 5FWkiqNnyMmksSmZ6iBbCCxc9X6sGEeInAhlENlIaOVfTTw5SuctomSc7jvpys2Y5tPSglFebse ltlOawAbs/yx7 X-Received: by 2002:a50:d9c5:: with SMTP id x5mr55010496edj.37.1634649588996; Tue, 19 Oct 2021 06:19:48 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyxJEkwLJU4fjorpFfvz3YyQo5eQqNpJmgnJuL4VTG8eyEZ+Hrx+U6t4pzRDOHn4SY0DXnhDA== X-Received: by 2002:a50:d9c5:: with SMTP id x5mr55010459edj.37.1634649588711; Tue, 19 Oct 2021 06:19:48 -0700 (PDT) Received: from krava ([83.240.63.48]) by smtp.gmail.com with ESMTPSA id f19sm11312559edj.77.2021.10.19.06.19.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Oct 2021 06:19:48 -0700 (PDT) Date: Tue, 19 Oct 2021 15:19:46 +0200 From: Jiri Olsa To: Steven Rostedt Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Subject: Re: [PATCH 7/8] ftrace: Add multi direct modify interface Message-ID: References: <20211008091336.33616-1-jolsa@kernel.org> <20211008091336.33616-8-jolsa@kernel.org> <20211014162819.5c85618b@gandalf.local.home> <20211015100509.78d4fb01@gandalf.local.home> <20211018221015.3f145843@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211018221015.3f145843@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Oct 18, 2021 at 10:10:15PM -0400, Steven Rostedt wrote: > On Sat, 16 Oct 2021 13:39:55 +0200 > Jiri Olsa wrote: > > > On Fri, Oct 15, 2021 at 10:05:09AM -0400, Steven Rostedt wrote: > > > On Fri, 15 Oct 2021 14:05:25 +0200 > > > Jiri Olsa wrote: > > > > > > > ATM I'm bit stuck on the bpf side of this whole change, I'll test > > > > it with my other changes when I unstuck myself ;-) > > > > > > If you want, I'll apply this as a separate change on top of your patch set. > > > As I don't see anything wrong with your current code. > > > > > > And when you are satisfied with this, just give me a "tested-by" and I'll > > > push it too. > > > > sounds great, thanks > > jirka > > Would you want to ack/review this? hum, do you have it in some branch already? I'm getting: patching file kernel/trace/ftrace.c Hunk #1 succeeded at 5521 with fuzz 1 (offset -40 lines). Hunk #2 FAILED at 5576. Hunk #3 succeeded at 5557 (offset -44 lines). 1 out of 3 hunks FAILED -- saving rejects to file kernel/trace/ftrace.c.rej when trying to apply on top of my changes thanks, jirka > > -- Steve > > From: "Steven Rostedt (VMware)" > Subject: [PATCH] ftrace/direct: Do not disable when switching direct callers > > Currently to switch a set of "multi" direct trampolines from one > trampoline to another, a full shutdown of the current set needs to be > done, followed by an update to what trampoline the direct callers would > call, and then re-enabling the callers. This leaves a time when the > functions will not be calling anything, and events may be missed. > > Instead, use a trick to allow all the functions with direct trampolines > attached will always call either the new or old trampoline while the > switch is happening. To do this, first attach a "dummy" callback via > ftrace to all the functions that the current direct trampoline is attached > to. This will cause the functions to call the "list func" instead of the > direct trampoline. The list function will call the direct trampoline > "helper" that will set the function it should call as it returns back to > the ftrace trampoline. > > At this moment, the direct caller descriptor can safely update the direct > call trampoline. The list function will pick either the new or old > function (depending on the memory coherency model of the architecture). > > Now removing the dummy function from each of the locations of the direct > trampoline caller, will put back the direct call, but now to the new > trampoline. > > A better visual is: > > [ Changing direct call from my_direct_1 to my_direct_2 ] > > : > call my_direct_1 > > |||||||||||||||||||| > vvvvvvvvvvvvvvvvvvvv > > : > call ftrace_caller > > : > [..] > call ftrace_ops_list_func > > ftrace_ops_list_func() > { > ops->func() -> direct_helper -> set rax to my_direct_1 or my_direct_2 > } > > call rax (to either my_direct_1 or my_direct_2 > > |||||||||||||||||||| > vvvvvvvvvvvvvvvvvvvv > > : > call my_direct_2 > > Link: https://lore.kernel.org/all/20211014162819.5c85618b@gandalf.local.home/ > > Signed-off-by: Steven Rostedt (VMware) > --- > kernel/trace/ftrace.c | 33 ++++++++++++++++++++------------- > 1 file changed, 20 insertions(+), 13 deletions(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 30120342176e..7ad1e8ae5855 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -5561,8 +5561,12 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_direct_multi); > */ > int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr) > { > - struct ftrace_hash *hash = ops->func_hash->filter_hash; > + struct ftrace_hash *hash; > struct ftrace_func_entry *entry, *iter; > + static struct ftrace_ops tmp_ops = { > + .func = ftrace_stub, > + .flags = FTRACE_OPS_FL_STUB, > + }; > int i, size; > int err; > > @@ -5572,21 +5576,22 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr) > return -EINVAL; > > mutex_lock(&direct_mutex); > - mutex_lock(&ftrace_lock); > + > + /* Enable the tmp_ops to have the same functions as the direct ops */ > + ftrace_ops_init(&tmp_ops); > + tmp_ops.func_hash = ops->func_hash; > + > + err = register_ftrace_function(&tmp_ops); > + if (err) > + goto out_direct; > > /* > - * Shutdown the ops, change 'direct' pointer for each > - * ops entry in direct_functions hash and startup the > - * ops back again. > - * > - * Note there is no callback called for @ops object after > - * this ftrace_shutdown call until ftrace_startup is called > - * later on. > + * Now the ftrace_ops_list_func() is called to do the direct callers. > + * We can safely change the direct functions attached to each entry. > */ > - err = ftrace_shutdown(ops, 0); > - if (err) > - goto out_unlock; > + mutex_lock(&ftrace_lock); > > + hash = ops->func_hash->filter_hash; > size = 1 << hash->size_bits; > for (i = 0; i < size; i++) { > hlist_for_each_entry(iter, &hash->buckets[i], hlist) { > @@ -5597,10 +5602,12 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr) > } > } > > - err = ftrace_startup(ops, 0); > + /* Removing the tmp_ops will add the updated direct callers to the functions */ > + unregister_ftrace_function(&tmp_ops); > > out_unlock: > mutex_unlock(&ftrace_lock); > + out_direct: > mutex_unlock(&direct_mutex); > return err; > } > -- > 2.31.1 >