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From: Rusty Russell <rusty@rustcorp.com.au>
To: Peter Zijlstra <peterz@infradead.org>, mingo@kernel.org,
        mathieu.desnoyers@efficios.com, oleg@redhat.com,
        paulmck@linux.vnet.ibm.com,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: linux-kernel@vger.kernel.org, andi@firstfloor.org, rostedt@goodmis.org,
        tglx@linutronix.de, peterz@infradead.org
Subject: Re: [RFC][PATCH 2/9] module: Sanitize RCU usage and locking
In-Reply-To: <20150228213109.952835328@infradead.org>
References: <20150228212447.381543289@infradead.org> <20150228213109.952835328@infradead.org>
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Date: Mon, 02 Mar 2015 21:46:45 +1030
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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.

That one is *specifically* a best effort bandaid for the case where
module initialization has failed.  It's theoretically racy, so we wait a
bit before freeing.

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.

Thanks,
Rusty.