From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) (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 620E92EBBA9; Wed, 8 Apr 2026 02:13:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775614407; cv=none; b=CClrtaStRdEmatq0sF3cZOqNlMwsqBob5hiJABmY00cH7/AinMk5Nva6ErGogEBKPNN9n8SsgPHEsOrtqrnCB6ehdCp7qd8a6L4NNboKzzHTC10ikCoZetw5cguk5PAwscFGJFxAhtzD0YbVOKgkkmRUjDzx+2ro2NQAAwArCdo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775614407; c=relaxed/simple; bh=BUWd4Pkdr/VZ3J3Hc+of4N0wwIWMVZrZaA8S2sS/YsY=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=huKfRARY+metuLmUfBdRF/Em8/m6SjurjMEd55PKdwW2c7m74DUS9cvEt1Ut8duPKn43zl6cY3/Fq/RIheLPoP7mdhFNLMRUBO8aC22vYIYomxo832gI1WPYgoRZCrHqA7Tw+vBaJr/H9uk/WHgO/peyRyyu1G9qjTbs4vEw7CA= 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=216.40.44.11 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 omf02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id BCC3D5BD13; Wed, 8 Apr 2026 02:13:24 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf02.hostedemail.com (Postfix) with ESMTPA id DE09080012; Wed, 8 Apr 2026 02:13:22 +0000 (UTC) Date: Tue, 7 Apr 2026 22:14:37 -0400 From: Steven Rostedt To: Pengpeng Hou Cc: Masami Hiramatsu , Mathieu Desnoyers , Tom Zanussi , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] tracing/hist: rebuild full_name on each hist_field_name() call Message-ID: <20260407221437.786b42f7@gandalf.local.home> In-Reply-To: <20260408101500.1-tracing-hist-reachability-reply-pengpeng@iscas.ac.cn> References: <20260329030950.32503-1-pengpeng@iscas.ac.cn> <20260401112224.85582-1-pengpeng@iscas.ac.cn> <20260408101500.1-tracing-hist-reachability-reply-pengpeng@iscas.ac.cn> 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: 7ua78i65ng6m7xyqape3o1jknazfs8x7 X-Rspamd-Server: rspamout02 X-Rspamd-Queue-Id: DE09080012 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/u6ec8ZlcsXasoW3W3Sj4itW2JK48i4r0= X-HE-Tag: 1775614402-888767 X-HE-Meta: U2FsdGVkX19B8oa3pBIYX8O+tS9HGxblgezriBpEaCPjUyIYxfg4awsr3Qg6hB9oQ17K5wd1/amZhEZOIPw7Cp58736QvdBhgzVKAb17wW8CG8/G30a4NizcZX0LjxCiuJ+F7sfyWh/yRaPiio1UJRAHT7G23i6zqB+z1Z+Y6rhWDgQ9NdioW8RSD0auNlc68SJ9dmpQ7sQhLI9/kfaWUcMg6nEy8QLYIV1+5o80hoysnsRzDlulac8DnldPjytwajLq7GEPzzbcCxQE2Pydji1TEbTpzjK8JwW53ERnDU604c6CU91KLSI8yJmMZEsn On Wed, 8 Apr 2026 10:15:00 +0800 Pengpeng Hou wrote: > Hi Steve, > > Thanks for looking at this. > > I believe this path is reachable. > > field->system is set when a VAR_REF is created with an event-qualified > reference. The assignment happens in init_var_ref(), which is called > from create_var_ref(). > > The parser accepts fully qualified references of the form > > system.event.$var > > and parse_expr() passes the parsed system/event strings into > create_var_ref(). trace_action_create() also accepts explicitly > qualified action parameters in the same form and passes those strings > into create_var_ref(). > > This is also documented in Documentation/trace/histogram.rst: > > fully-qualified name is of the form 'system.event_name.$var_name' > or 'system.event_name.field'. Ah I read the document and missed this part. Thanks for pointing it out. None of our tests use this, so that definitely needs to be fixed. OK, yeah I can trigger that path now. I'll continue looking at the patch. Thanks, -- Steve > > The path is user-visible because reading back the trigger goes through > > event_hist_trigger_print() -> hist_field_print() -> hist_field_name() > > so creating a hist trigger that uses an inter-event variable reference > in fully qualified form is enough to exercise it. > > So I don't think this is dead code. If you would prefer a different way > of handling the printed name, I can respin accordingly, but I don't > think the current branch is unreachable. > > Thanks, > Pengpeng >