linux-kernel - Re: [patch 06/10] Text Edit Lock - kprobes architecture independent support

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Message-ID: <20070907102805.GA10389@in.ibm.com>
Date:	Fri, 7 Sep 2007 15:58:05 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	prasanna@...ibm.com, anil.s.keshavamurthy@...el.com,
	davem@...emloft.net
Subject: Re: [patch 06/10] Text Edit Lock - kprobes architecture independent support

On Thu, Sep 06, 2007 at 04:01:30PM -0400, Mathieu Desnoyers wrote:

<snip>

> @@ -716,8 +720,9 @@ static int __kprobes pre_handler_kretpro
>  				 struct kretprobe_instance, uflist);
>  		ri->rp = rp;
>  		ri->task = current;
> +		kernel_text_lock();
>  		arch_prepare_kretprobe(ri, regs);
> -
> +		kernel_text_unlock();

pre_handler_kretprobe() is run when the entry probe for a retprobed
function is hit and cannot block. You can't take a mutex here.

And why do we need to take the kernel_text_lock() here anyway? All
arch_prepare_kretprobe() does is modify the return address stored either
on stack or a register (arch specific) to the trampoline. We don't
change any kernel text here.

Ananth
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