From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) (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 D2D5B350D47; Wed, 7 Jan 2026 16:41:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767804083; cv=none; b=qfKPsdVQ4nXkFXp8mLjta3UWygDsErF4q8gwy+1wjl8lEEjnk40l5v0ZdJe/D/Gu3uquS042dMhEPULUPV4tf5DEY/t0aLuycmHzqQpu6jBRDinoMhjSDAhpBFNGg58uusoAhUQ6NtgHhQnxx11HTH6YDR9T+VJMdSEwsMrSzvU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767804083; c=relaxed/simple; bh=631rQmD14PsFiLcLYmVUk2mt1AYrLAqIkXqnb4mT/6A=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=jYRj4FS8riRyVz4sQHUTdQBuvFhFF7tOW82Pzen1V8ZJ9yviQeNb1ft9xLd2knCvKdvtdBfmsY/MdIrrtZ6DTwz+tzNCwhXhfHg+PZBdYiswWImqDRyllM3XG6bupXIKakSgphLZ7f6nqSKp0BVcdIlDqTiEgB95k/Mi9I6wlHQ= 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=216.40.44.13 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 omf10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id E56BF58EE5; Wed, 7 Jan 2026 16:41:07 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf10.hostedemail.com (Postfix) with ESMTPA id 3D5B32F; Wed, 7 Jan 2026 16:41:06 +0000 (UTC) Date: Wed, 7 Jan 2026 11:41:33 -0500 From: Steven Rostedt To: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] tracing: Make the backup instance readonly Message-ID: <20260107114133.7f14dac2@gandalf.local.home> In-Reply-To: <176779715937.4193242.8486149802702305279.stgit@mhiramat.tok.corp.google.com> References: <176779714767.4193242.1978666866487010024.stgit@mhiramat.tok.corp.google.com> <176779715937.4193242.8486149802702305279.stgit@mhiramat.tok.corp.google.com> X-Mailer: Claws Mail 3.20.0git84 (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 X-Stat-Signature: 7bu9wi7f3nbwq96k5k39bwx7azy3nxx8 X-Rspamd-Server: rspamout03 X-Rspamd-Queue-Id: 3D5B32F X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19BACx7bnSlk1elzuN6a9ELkiguqwHsPZU= X-HE-Tag: 1767804066-827929 X-HE-Meta: U2FsdGVkX1+d9KRflcF4ib1jOYg5It9K1hTz1RtFmf0IDqge7Wu5gR/LdFCABEEbLBx3d9WAlOTM75Ol6j4dW2xgmUsq8FUFilf02qwflR49eJ6OUAR49Kgczy24Dq8tUFoiQMsMNdXpYJu+XMFPNUyW2yZ3sHqK5IF5c/TOoqJn18sAIwm28n1U4GY6M3f88c7abE2clSf9VsAofe5mJt1oJQ1OCIDJAvXIJPvu4C6su2xX19zI82WAOoYmWBjGEIeBhtmmNdRwK+2KKx3U7BNJdAUG+6SuVgpmnZcmvgooRWaIG/gRbcSaWe5Soe9fOFtZEe2rVaKPaE6ofly9hRiJeE/t6v77 On Wed, 7 Jan 2026 23:45:59 +0900 "Masami Hiramatsu (Google)" wrote: > From: Masami Hiramatsu (Google) > > Since there is no reason to reuse the backup instance, make it > readonly. Note that only backup instances are readonly, because > other trace instances will be empty unless it is writable. > Only backup instances have copy entries from the original. > > Signed-off-by: Masami Hiramatsu (Google) > --- > kernel/trace/trace.c | 91 ++++++++++++++++++++++++++++++++----------- > kernel/trace/trace.h | 6 +++ > kernel/trace/trace_events.c | 14 +++++-- > 3 files changed, 84 insertions(+), 27 deletions(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 38f7a7a55c23..725930f5980e 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -4888,6 +4888,9 @@ static int tracing_open(struct inode *inode, struct file *file) > int cpu = tracing_get_cpu(inode); > struct array_buffer *trace_buf = &tr->array_buffer; > > + if (trace_array_is_readonly(tr)) > + return -EPERM; So this fails if someone opens a file in RDONLY mode? Why? > + > #ifdef CONFIG_TRACER_MAX_TRACE > if (tr->current_trace->print_max) > trace_buf = &tr->max_buffer; > @@ -6077,6 +6080,9 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr, > ssize_t tracing_resize_ring_buffer(struct trace_array *tr, > unsigned long size, int cpu_id) > { > + if (trace_array_is_readonly(tr)) > + return -EPERM; In fact, I don't think we need any of these. > + > guard(mutex)(&trace_types_lock); > > if (cpu_id != RING_BUFFER_ALL_CPUS) { > @@ -9353,12 +9381,16 @@ static void > tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) > { > struct dentry *d_percpu = tracing_dentry_percpu(tr, cpu); > + umode_t writable_mode = TRACE_MODE_WRITE; > struct dentry *d_cpu; > char cpu_dir[30]; /* 30 characters should be more than enough */ > > if (!d_percpu) > return; > > + if (trace_array_is_readonly(tr)) > + writable_mode = TRACE_MODE_READ; This is more like what we should do with all the files in a read-only instance. Just make all files not allow writes. We may need to make sure they can't be changed to write as well. But that will require a change to tracefs (and eventfs). -- Steve > + > snprintf(cpu_dir, 30, "cpu%ld", cpu); > d_cpu = tracefs_create_dir(cpu_dir, d_percpu); > if (!d_cpu) { > @@ -9371,7 +9403,7 @@ tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) > tr, cpu, &tracing_pipe_fops); > > /* per cpu trace */ > - trace_create_cpu_file("trace", TRACE_MODE_WRITE, d_cpu, > + trace_create_cpu_file("trace", writable_mode, d_cpu, > tr, cpu, &tracing_fops); > > trace_create_cpu_file("trace_pipe_raw", TRACE_MODE_READ, d_cpu,