linux-kernel - Re: [PATCH] arm64: replace read_lock to rcu lock in call_break

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Message-ID: <20151001150735.GH6963@e104818-lin.cambridge.arm.com>
Date:	Thu, 1 Oct 2015 16:07:35 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Yang Shi <yang.shi@...aro.org>
Cc:	rostedt@...dmis.org, will.deacon@....com, dave.long@...aro.org,
	panand@...hat.com, linaro-kernel@...ts.linaro.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-rt-users@...r.kernel.org
Subject: Re: [PATCH] arm64: replace read_lock to rcu lock in call_break_hook

On Wed, Sep 30, 2015 at 03:59:04PM -0700, Yang Shi wrote:
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index cebf786..eb520d0 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -292,11 +292,11 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr)
>  	struct break_hook *hook;
>  	int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
>  
> -	read_lock(&break_hook_lock);
> +	rcu_read_lock();
>  	list_for_each_entry(hook, &break_hook, node)
>  		if ((esr & hook->esr_mask) == hook->esr_val)
>  			fn = hook->fn;
> -	read_unlock(&break_hook_lock);
> +	rcu_read_unlock();
>  
>  	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
>  }

That's not enough, you also need list_(add|del)_rcu where the list is
modified, together with list_for_each_entry_rcu() here.

-- 
Catalin
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