linux-kernel - Re: cgroup trace events acquire sleeping locks

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Message-ID: <20180710092635.GD2476@hirez.programming.kicks-ass.net>
Date:   Tue, 10 Jul 2018 11:26:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        tglx@...utronix.de, Clark Williams <williams@...hat.com>,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: cgroup trace events acquire sleeping locks

On Mon, Jul 09, 2018 at 04:30:10PM -0400, Steven Rostedt wrote:
> On Mon, 9 Jul 2018 22:22:15 +0200
> Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
> 
> > On 2018-07-09 15:01:54 [-0400], Steven Rostedt wrote:
> > > > which is the trace_cgroup_rmdir() trace event in cgroup_rmdir(). The
> > > > trace event invokes cgroup_path() which acquires a spin_lock_t and this
> > > > is invoked within a preempt_disable()ed section.   
> > > 
> > > Correct. And I wish no trace event took spin locks.  
> > 
> > is there an easy way to detect this? I mean instead hitting the trace
> > event with debug enabled and doing a review of each of them.
> 
> Hmm, good question. I could possibly make all the tracepoint code into
> its own section. And then look to see if any spin locks exist in them.
> That wouldn't be too trivial to implement though.

pick a bit from the preempt_count (say right above NMI_MASK) and set it
inside a trace-event and add in_trace().

Then make lockdep explode when in_trace().

Or something along those lines.