linux-kernel - Re: [PATCH v2] tracing: Introduce pipe_cpumask to avoid race on trace

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Message-ID: <20230818115322.3dfda470@gandalf.local.home>
Date:   Fri, 18 Aug 2023 11:53:22 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Zheng Yejian <zhengyejian1@...wei.com>, <laijs@...fujitsu.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tracing: Introduce pipe_cpumask to avoid race on
 trace_pipes

On Fri, 18 Aug 2023 23:23:01 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> It uses trace_pipe_raw. I guess if splice(from trace_pipe_raw to virtio-serial)
> returns -1 and errno == EAGAIN, the trace data will be lost?

It shouldn't. If it does, then there's likely a bug. The code will block
and if an interrupt comes in it will return immediately without reading
from the buffer.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/trace.c#n8262

I don't see where it would return -EINTR and consume data, but I may be
missing something.

-- Steve