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Date: Mon, 2 Mar 2015 13:37:18 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: mingo@kernel.org, mathieu.desnoyers@efficios.com, oleg@redhat.com,
        paulmck@linux.vnet.ibm.com,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        linux-kernel@vger.kernel.org, andi@firstfloor.org, rostedt@goodmis.org,
        tglx@linutronix.de
Subject: Re: [RFC][PATCH 2/9] module: Sanitize RCU usage and locking
Message-ID: <20150302123718.GL21418@twins.programming.kicks-ass.net>
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On Mon, Mar 02, 2015 at 09:46:45PM +1030, Rusty Russell wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
> > Currently the RCU usage in module is an inconsistent mess of RCU and
> > RCU-sched, this is broken for CONFIG_PREEMPT where synchronize_rcu()
> > does not imply synchronize_sched().
> 
> Huh?  It's not "an inconsistent mess".  They're all synchronize_rcu(),
> except one.

Uhm, most of them use preempt_disable(), which is RCU-sched, not RCU.

The only RCU user I found was the bug-list thing.

What other RCU users are there?

> That said, I love the new checks, thanks!
> 
> > +static inline void module_assert_mutex(void)
> > +{
> > +	lockdep_assert_held(&module_mutex);
> > +}
> > +
> > +static inline void module_assert_mutex_or_preempt(void)
> > +{
> > +#ifdef CONFIG_LOCKDEP
> > +	int rcu_held = rcu_read_lock_sched_held();
> > +	int mutex_held = 1;
> > +
> > +	if (debug_locks)
> > +		mutex_held = lockdep_is_held(&module_mutex);
> > +
> > +	WARN_ON(!rcu_held && !mutex_held);
> > +#endif
> > +}
> 
> Minor nitpick: I generally avoid static inline in C files (unless
> functions are unused under some config options, which these aren't).
> 
> In general, they mess up future cleanups, as gcc doesn't warn about
> unused functions.

Ah, sure. And I suppose gcc will not emit code for empty static
functions anyhow - which is the reason I stuck the inline on, to avoid
it generating code for the !LOCKDEP case.