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Date: Wed, 8 Aug 2018 08:46:29 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Joel Fernandes <joelaf@...gle.com>
Cc: Joel Fernandes <joel@...lfernandes.org>,
LKML <linux-kernel@...r.kernel.org>,
"Cc: Android Kernel" <kernel-team@...roid.com>,
Boqun Feng <boqun.feng@...il.com>,
Byungchul Park <byungchul.park@....com>,
Ingo Molnar <mingo@...hat.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Namhyung Kim <namhyung@...nel.org>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Glexiner <tglx@...utronix.de>,
Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and
unify their usage
On Tue, 7 Aug 2018 20:53:54 -0700
Joel Fernandes <joelaf@...gle.com> wrote:
> > When I talked to Paul few months ago about SRCU from NMI context, he
> > mentioned the per-cpu memory operations during srcu_read_lock can be
> > NMI interrupted, that's why we added that warning.
>
> So I looked more closely, __srcu_read_lock on 2 different handles may
> still be doing a this_cpu_inc on the same location..
> (sp->sda->srcu_lock_count). :-(
>
> Paul any ideas on how to solve this?
>
> It does start to seem like a show stopper :-(
What's wrong with a this_cpu_inc()? It's atomic for the CPU. Although
it wont be atomic for the capture of the idx. But I also don't see
interrupts being disabled, thus an NMI is no different than any
interrupt doing the same thing, right?
-- Steve
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