From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D8B6924169E; Tue, 8 Apr 2025 23:37:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744155424; cv=none; b=Mn/9ZTD/d/3ljGme3hBwYPLB29qqynzfaaSfNcQDXlU1eXTnJLKMVSOxlciujlLX6B4zS0HC2lIhTp1IvXzMoEwSXpROT/+d8n9wQ2BwhNAe6RG/mJst2wcfyWy/y3XoMVrw0/w4MEAcxwGxt5RNnLclZYoGGa6e+mDtv2Q+gM0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744155424; c=relaxed/simple; bh=qeBpWOGfbzJOiCA+hJbPkYPDneCqlrg4wZjdvh8DyT0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=Kbvh9MqFXFSdadMvrPQn6T4QYo8Av4xaWjT4DfEUEVyrIKswRvGqQk9/8zSlX5AsPbbHRSice00DfWm3YC0sj7b5WnV+Aqnl18d91vVDq2o9Ddv2xiC7SNZAhi+tSFqzQ7vseztrKCUIPAnz3uLkeh9Bk2hBt8oCuhj+aw3Uvms= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mJaDqAgD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mJaDqAgD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 725E8C4CEE5; Tue, 8 Apr 2025 23:37:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744155424; bh=qeBpWOGfbzJOiCA+hJbPkYPDneCqlrg4wZjdvh8DyT0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=mJaDqAgDhT7NyTXj0SNQLNfYR7g62SMYxdeXXe5/AGznNqblaZmLUyyXNFVObzMoC dxn0Fihnox9zkhwzcwqXZBoAsQqDlvjQiA/1MPOs9elK8RBNTYCtcfz4KoD2cpdyHa M9NhRTmyLCwMbIn9mqTr7IBkYCUjkUisDotcUK0oxc5oyQfmALq9fm9w5aBRV/VfLr rtsJtkzbPDeh7owLrrA9ipR6pCTiM4kO6nBBVxdw2wfp4V9oIl94p7Uc7HT7070uMg AAaUHoSjTTBKs2fDWAmvL1eZCYVC3fLnnrY/1bM1RSVcnr/69BkWA56sf7VmKreatV rb+nqmNQsAvTw== Date: Wed, 9 Apr 2025 08:36:58 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt Cc: LKML , Linux Trace Kernel , Masami Hiramatsu , Mathieu Desnoyers , Tom Zanussi , Douglas Raillard Subject: Re: [PATCH] tracing: Do not add length to print format in synthetic events Message-Id: <20250409083658.25c2687da3fad617514f8b22@kernel.org> In-Reply-To: <20250407154139.69955768@gandalf.local.home> References: <20250407154139.69955768@gandalf.local.home> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-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 On Mon, 7 Apr 2025 15:41:39 -0400 Steven Rostedt wrote: > From: Steven Rostedt > > The following causes a vsnprintf fault: > > # echo 's:wake_lat char[] wakee; u64 delta;' >> /sys/kernel/tracing/dynamic_events > # echo 'hist:keys=pid:ts=common_timestamp.usecs if !(common_flags & 0x18)' > /sys/kernel/tracing/events/sched/sched_waking/trigger > # echo 'hist:keys=next_pid:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,next_comm,$delta)' > /sys/kernel/tracing/events/sched/sched_switch/trigger > > Because the synthetic event's "wakee" field is created as a dynamic string > (even though the string copied is not). The print format to print the > dynamic string changed from "%*s" to "%s" because another location > (__set_synth_event_print_fmt()) exported this to user space, and user > space did not need that. But it is still used in print_synth_event(), and > the output looks like: > > -0 [001] d..5. 193.428167: wake_lat: wakee=(efault)sshd-sessiondelta=155 > sshd-session-879 [001] d..5. 193.811080: wake_lat: wakee=(efault)kworker/u34:5delta=58 > -0 [002] d..5. 193.811198: wake_lat: wakee=(efault)bashdelta=91 > bash-880 [002] d..5. 193.811371: wake_lat: wakee=(efault)kworker/u35:2delta=21 > -0 [001] d..5. 193.811516: wake_lat: wakee=(efault)sshd-sessiondelta=129 > sshd-session-879 [001] d..5. 193.967576: wake_lat: wakee=(efault)kworker/u34:5delta=50 > > The length isn't needed as the string is always nul terminated. Just print > the string and not add the length (which was hard coded to the max string > length anyway). > Good catch! Acked-by: Masami Hiramatsu (Google) Thanks! > Cc: stable@vger.kernel.org > Fixes: 4d38328eb442d ("tracing: Fix synth event printk format for str fields"); > Signed-off-by: Steven Rostedt (Google) > --- > kernel/trace/trace_events_synth.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c > index 969f48742d72..33cfbd4ed76d 100644 > --- a/kernel/trace/trace_events_synth.c > +++ b/kernel/trace/trace_events_synth.c > @@ -370,7 +370,6 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter, > union trace_synth_field *data = &entry->fields[n_u64]; > > trace_seq_printf(s, print_fmt, se->fields[i]->name, > - STR_VAR_LEN_MAX, > (char *)entry + data->as_dynamic.offset, > i == se->n_fields - 1 ? "" : " "); > n_u64++; > -- > 2.47.2 > -- Masami Hiramatsu (Google)