linux-kernel - Re: [PATCH v3 4/7] kprobes: Replace %p with other pointer types

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Date:   Fri, 27 Apr 2018 08:56:36 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Ananth N Mavinakayanahalli <ananth@...ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jon Medhurst <tixy@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "Tobin C . Harding" <me@...in.cc>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        akpm@...ux-foundation.org, acme@...nel.org, rostedt@...dmis.org,
        brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v3 4/7] kprobes: Replace %p with other pointer types


* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> @@ -712,7 +712,7 @@ static void reuse_unused_kprobe(struct kprobe *ap)
>  	op = container_of(ap, struct optimized_kprobe, kp);
>  	if (unlikely(list_empty(&op->list)))
>  		printk(KERN_WARNING "Warning: found a stray unused "
> -			"aggrprobe@%p\n", ap->addr);
> +			"aggrprobe@%pS\n", ap->addr);

Is this a kernel bug? If yes then please convert this to a WARN_ON_ONCE() that 
doesn't print any kernel addresses.

>  	/* Enable the probe again */
>  	ap->flags &= ~KPROBE_FLAG_DISABLED;
>  	/* Optimize it again (remove from op->list) */
> @@ -985,7 +985,8 @@ static int arm_kprobe_ftrace(struct kprobe *p)
>  	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
>  				   (unsigned long)p->addr, 0, 0);
>  	if (ret) {
> -		pr_debug("Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret);
> +		pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
> +			 p->addr, ret);
>  		return ret;

Can this happen during normal use? If yes then just remove the warning message.

>  	}
>  
> @@ -1025,7 +1026,8 @@ static int disarm_kprobe_ftrace(struct kprobe *p)
>  
>  	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
>  			   (unsigned long)p->addr, 1, 0);
> -	WARN(ret < 0, "Failed to disarm kprobe-ftrace at %p (%d)\n", p->addr, ret);
> +	WARN(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
> +	     p->addr, ret);

As this is a signal of a kernel bug, just convert this to a regular WARN_ONCE() 
that doesn't print any kernel addresses.

> +/* Caller must NOT call this in usual path. This is only for critical case */
>  void dump_kprobe(struct kprobe *kp)
>  {
> -	printk(KERN_WARNING "Dumping kprobe:\n");
> -	printk(KERN_WARNING "Name: %s\nAddress: %p\nOffset: %x\n",
> -	       kp->symbol_name, kp->addr, kp->offset);
> +	pr_err("Dumping kprobe:\n");
> +	pr_err("Name: %s\nOffset: %x\nAddress: %pS\n",
> +	       kp->symbol_name, kp->offset, kp->addr);

No, this function should just go away and be replaced by a WARN() in 
reenter_kprobe().

Thanks,

	Ingo