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Message-ID: <CAJWu+oqPUuF4rFOQ8=G3+ZxXJxiiNRBYE8C=zZ93A8qA+muHEg@mail.gmail.com>
Date: Tue, 7 Aug 2018 20:53:54 -0700
From: Joel Fernandes <joelaf@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
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, Aug 7, 2018 at 8:44 PM, Joel Fernandes <joelaf@...gle.com> wrote:
> Hi Steve,
>
> On Tue, Aug 7, 2018 at 7:28 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
[...]
>>> @@ -171,8 +174,7 @@ extern void syscall_unregfunc(void);
>>> } while ((++it_func_ptr)->func); \
>>> } \
>>> \
>>> - if (rcuidle) \
>>> - srcu_read_unlock_notrace(&tracepoint_srcu, idx);\
>>> + srcu_read_unlock_notrace(ss, idx); \
>>
>> Hmm, why do we have the two different srcu handles?
>
> Because if the memory operations happening on the normal SRCU handle
> (during srcu_read_lock) is interrupted by NMI, then the other handle
> (devoted to NMI) could be used instead and not bother the interrupted
> handle. Does that makes sense?
>
> 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 :-(
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