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

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Message-Id: <20170517103834.5e8642a26e2e49369c88bf0d@kernel.org>
Date:   Wed, 17 May 2017 10:38:34 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: WARNING at arch/x86/kernel/alternative.c:707
 text_poke+0x25d/0x270

On Tue, 16 May 2017 23:42:58 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Wed, 17 May 2017, Masami Hiramatsu wrote:
> > On Tue, 16 May 2017 09:48:02 -0400
> > Steven Rostedt <rostedt@...dmis.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...
> 
> Find below the patch I'm using for now .

Thank you very much! It looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

> 
> Thanks,
> 
> 	tglx
> 
> 8<--------------------
> 
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -349,6 +349,9 @@ extern int proc_kprobes_optimization_han
>  					     int write, void __user *buffer,
>  					     size_t *length, loff_t *ppos);
>  #endif
> +extern void wait_for_kprobe_optimizer(void);
> +#else
> +static inline void wait_for_kprobe_optimizer(void) { }
>  #endif /* CONFIG_OPTPROBES */
>  #ifdef CONFIG_KPROBES_ON_FTRACE
>  extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -595,7 +595,7 @@ static void kprobe_optimizer(struct work
>  }
>  
>  /* Wait for completing optimization and unoptimization */
> -static void wait_for_kprobe_optimizer(void)
> +void wait_for_kprobe_optimizer(void)
>  {
>  	mutex_lock(&kprobe_mutex);
>  
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1535,6 +1535,11 @@ static __init int kprobe_trace_self_test
>  
>  end:
>  	release_all_trace_kprobes();
> +	/*
> +	 * Wait for the optimizer work to finish. Otherwise it might fiddle
> +	 * with probes in already freed __init text.
> +	 */
> +	wait_for_kprobe_optimizer();
>  	if (warn)
>  		pr_cont("NG: Some tests are failed. Please check them.\n");
>  	else


-- 
Masami Hiramatsu <mhiramat@...nel.org>