From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9224F357719; Thu, 18 Dec 2025 15:39:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766072401; cv=none; b=WOpqFvxjoRhrjqdfNJOlNB9EYygkxJDeHZga3Td3MMZt6wOqFFzEDAiIsl1rb0kZMkiZgoQQdaywqPS/0stAeT5RfanvIhWoVcMDgCiuisr6TFIHfHnPVVjSyi+vWhJffVYDH7FcLt4l7FhfBCKxzzshQRIyt+YqNXTW/ZivLaY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766072401; c=relaxed/simple; bh=4XQw+STsrMN9eUhH3fzOAd2bq6FCEKqXxK0hHCazLDA=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=HE4Vz4CqtsMcftgdHyRcxODG4I0+6vOLYTGJmK7tZjPB6SlSd024dVrZGd/mLQV6NdsMiYXQm2Y26qvaGeerVYGQ81h1Tfjb2TCXHtaeNepp9F5zTcq4uLWzMqfFO0PWItMxBK2vEwdYBliRHwHWSW+fUMfioZF+YEQA5+txU54= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 9F49FB7460; Thu, 18 Dec 2025 15:39:43 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf04.hostedemail.com (Postfix) with ESMTPA id CA3EF20030; Thu, 18 Dec 2025 15:39:40 +0000 (UTC) Date: Thu, 18 Dec 2025 10:41:19 -0500 From: Steven Rostedt To: Jiri Olsa Cc: Steven Rostedt , Florent Revest , Mark Rutland , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Menglong Dong , Song Liu Subject: Re: [PATCHv5 bpf-next 6/9] ftrace: Add update_ftrace_direct_mod function Message-ID: <20251218104119.311adc09@gandalf.local.home> In-Reply-To: <20251218101942.0716efd6@gandalf.local.home> References: <20251215211402.353056-1-jolsa@kernel.org> <20251215211402.353056-7-jolsa@kernel.org> <20251218101942.0716efd6@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: hyd7obcpethh7mbhynnfm913gwqf8351 X-Rspamd-Server: rspamout03 X-Rspamd-Queue-Id: CA3EF20030 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19eMCvXLU/iy0pusX2AKTnSYMMq1qf40Gk= X-HE-Tag: 1766072380-414909 X-HE-Meta: U2FsdGVkX1+qdFcnlxLPjXd3JW5Y/+0pKI0xTsAa/MHRhpHeNLBsPBRNCg+H723yVJ7NpyItko3gA2wj68SbZ+IIIPUnbgTsdXjs+Y7PsDCRAayGAvC07jcanonG5k/BqdK2mbkU6RW8quT4XG7lqEfa98717k59hUZx32RtbzwjJLWsT0COfK8CsxpWJ2i7qTsGKFwc27rM+cxfZS2ACZcTOBxcMJUO9UvJAddUjNXIjaePm+BcK9QaQk3KbmwUsEI8fbn3U7zMbyKF9fgl4qlXKekB4zCTfeTaOyO+N0wSbKub9HEdfqIh7n2Rt+eDv1pVRsL3czVsAhAgxXdwoUGgqBNDD21y8PlfQw1KcVe811+P9vQO7XHGsfDoJhMh6/twovBHduGQCg1ab28PDA== On Thu, 18 Dec 2025 10:19:42 -0500 Steven Rostedt wrote: > On Mon, 15 Dec 2025 22:13:59 +0100 > Jiri Olsa wrote: > > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > > index 48dc0de5f2ce..95a38fb18ed7 100644 > > --- a/kernel/trace/ftrace.c > > +++ b/kernel/trace/ftrace.c > > @@ -6489,6 +6489,78 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash) > > return err; > > } > > > > Kerneldoc needed. > > > +int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock) > > +{ > > + struct ftrace_func_entry *entry, *tmp; > > + static struct ftrace_ops tmp_ops = { > > + .func = ftrace_stub, > > + .flags = FTRACE_OPS_FL_STUB, > > + }; > > + struct ftrace_hash *orig_hash; > > + unsigned long size, i; > > + int err = -EINVAL; > > + > > + if (!hash_count(hash)) > > + return -EINVAL; > > + if (check_direct_multi(ops)) > > + return -EINVAL; > > + if (!(ops->flags & FTRACE_OPS_FL_ENABLED)) > > + return -EINVAL; > > + if (direct_functions == EMPTY_HASH) > > + return -EINVAL; > > + > > + if (do_direct_lock) > > + mutex_lock(&direct_mutex); > > This optional taking of the direct_mutex lock needs some serious rationale > and documentation. > > > + > > + orig_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL; > > + if (!orig_hash) > > + goto unlock; > > + > > + /* Enable the tmp_ops to have the same functions as the direct ops */ Add to the comments here: * In order to modify the direct callers, all the functions need to * first be calling the ftrace_ops_list_func() and not be connected * to any direct callers. To do that, create a temporary ops that * attach to the same functions as the direct ops, and attach that * first. Then when adding the direct ops, it will use the * ftrace_ops_list_func(), and this can safely modify what the * direct ops call. Or something like that. I want this code to be as clear as day to what it is doing. In a year or two, we will forget, and this will be very confusing to newcomers. > > + ftrace_ops_init(&tmp_ops); > > + tmp_ops.func_hash = ops->func_hash; > > + > > + err = register_ftrace_function_nolock(&tmp_ops); > > + if (err) > > + goto unlock; > > + > > + /* > > + * Call __ftrace_hash_update_ipmodify() here, so that we can call > > + * ops->ops_func for the ops. This is needed because the above > > + * register_ftrace_function_nolock() worked on tmp_ops. > > + */ > > + err = __ftrace_hash_update_ipmodify(ops, orig_hash, orig_hash, true); > > + if (err) > > + goto out; > > + > > + /* > > + * Now the ftrace_ops_list_func() is called to do the direct callers. > > + * We can safely change the direct functions attached to each entry. > > + */ > > + mutex_lock(&ftrace_lock); > > I'm going to need some time staring at this code. It looks like it may be > relying on some internals here. > > -- Steve > > > > + I would add a comment here: /* Now update the direct functions to point to the new callbacks */ -- Steve > > + size = 1 << hash->size_bits; > > + for (i = 0; i < size; i++) { > > + hlist_for_each_entry(entry, &hash->buckets[i], hlist) { > > + tmp = __ftrace_lookup_ip(direct_functions, entry->ip); > > + if (!tmp) > > + continue; > > + tmp->direct = entry->direct; > > + } > > + } > > + > > + mutex_unlock(&ftrace_lock); > > + > > +out: > > + /* Removing the tmp_ops will add the updated direct callers to the functions */ > > + unregister_ftrace_function(&tmp_ops); > > + > > +unlock: > > + if (do_direct_lock) > > + mutex_unlock(&direct_mutex); > > + return err; > > +} > > + > > #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */ > > > > /**