linux-kernel - Re: WARNING at arch/x86/kernel/alternative.c:707 text

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Date:   Tue, 16 May 2017 11:30:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: WARNING at arch/x86/kernel/alternative.c:707
 text_poke+0x25d/0x270

On Wed, 17 May 2017 00:15:39 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:


> > It appears that the kprobe_optimizer work thread call happened after
> > the init pages were freed, causing alternative.c to give the above
> > warning because the text that is being unoptimized happens to no longer
> > exist.  
> 
> Ah, I see. I need to check that case. Actually for the module
> init text area, kill_kprobe() correctly kicks kill_optimized_kprobe()
> so it should safe. But above case is on the init-text in kernel
> itself. I guess module_notifier may not be called for that area...

Hmm, what happens if you add a kprobe to a module, remove it, and then
remove the module. If the module is still loaded when it is removed,
wouldn't that cause the optimized probe to be delayed? Wouldn't that
open a race where the optimizer work queue can be called when no module
exists?

-- Steve