linux-kernel - Re: [PATCH v4 09/10] user_events: Optimize writing events by only copying data once

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Message-ID: <20211108182006.7b09a630@gandalf.local.home>
Date:   Mon, 8 Nov 2021 18:20:06 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, linux-trace-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 09/10] user_events: Optimize writing events by only
 copying data once

On Mon, 8 Nov 2021 15:17:10 -0800
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> > Which reminds me that trace_event_buffer_reserve() expects to be called
> > with preemption disabled. And I'm guessing that may not be the case for you.
> >   
> 
> Thanks, should be good there:
> I have rcu_read_lock_sched() held, which will have preemption disabled
> during the various probe calls.

Ah, that's right. Thanks for the reminder.

> 
> > I'll change this so that it always disables preemption even if it uses the
> > filter buffer, and *always* disables preemption on return.

Even so, I think it's better to have it consistently disable/enable
preemption than expect the caller to do so.

-- Steve