linux-kernel - Re: [PATCH v5 01/10] module: Sanitize RCU usage and locking

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Message-ID: <20150413153229.GA6040@gmail.com>
Date:	Mon, 13 Apr 2015 17:32:29 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	rusty@...tcorp.com.au, mathieu.desnoyers@...icios.com,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, rostedt@...dmis.org, tglx@...utronix.de,
	laijs@...fujitsu.com, linux@...izon.com
Subject: Re: [PATCH v5 01/10] module: Sanitize RCU usage and locking


* Peter Zijlstra <peterz@...radead.org> wrote:

> 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().
> 
> Most usage sites use preempt_{dis,en}able() which is RCU-sched, but
> (most of) the modification sites use synchronize_rcu(). With the
> exception of the module bug list, which actually uses RCU.
> 
> Convert everything over to RCU-sched.
> 
> Furthermore add lockdep asserts to all sites, because its not at all
> clear to me the required locking is observed, esp. on exported
> functions.

nit:

s/its/it's

> +static 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);

So because rcu_read_lock_sched_held() also depends on debug_locks 
being on to be fully correct, shouldn't the warning also be within the 
debug_locks condition?

> @@ -3106,11 +3128,11 @@ static noinline int do_init_module(struc
>  	mod->init_text_size = 0;
>  	/*
>  	 * We want to free module_init, but be aware that kallsyms may be
> +	 * walking this with preempt disabled.  In all the failure paths, we
> +	 * call synchronize_sched, but we don't want to slow down the success
> +	 * path, so use actual RCU here.

nit:

s/synchronize_sched
 /synchronize_sched()

Thanks,

	Ingo
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