linux-kernel - Re: [PATCH v11 3/3] tracing: Centralize preemptirq tracepoints and unify their usage

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Message-ID: <20180730191855.GA46892@joelaf.mtv.corp.google.com>
Date:   Mon, 30 Jul 2018 12:18:55 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Boqun Feng <boqun.feng@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Erick Reyes <erickreyes@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Julia Cartwright <julia@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Glexiner <tglx@...utronix.de>,
        Todd Kjos <tkjos@...gle.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v11 3/3] tracing: Centralize preemptirq tracepoints and
 unify their usage

On Mon, Jul 30, 2018 at 10:58:13AM +0200, Peter Zijlstra wrote:
> On Thu, Jul 26, 2018 at 04:50:44PM -0700, Joel Fernandes wrote:
> > One note, I have to check for lockdep recursion in the code that calls
> > the trace events API and bail out if we're in lockdep recursion
> > protection to prevent something like the following case: a spin_lock is
> > taken. Then lockdep_acquired is called.  That does a raw_local_irq_save
> > and then sets lockdep_recursion, and then calls __lockdep_acquired. In
> > this function, a call to get_lock_stats happens which calls
> > preempt_disable, which calls trace IRQS off somewhere which enters my
> > tracepoint code and sets the tracing_irq_cpu flag to prevent recursion.
> > This flag is then never cleared causing lockdep paths to never be
> > entered and thus causing splats and other bad things.
> 
> That is now fixed, right?

Yes, that's right it got fixed from v9->v10 but I forgot to update the
changelog, I'll make the change and resend. Thanks!

thanks,

- Joel