Message-ID: <54EC5160.7090400@hitachi.com>
Date: Tue, 24 Feb 2015 19:24:32 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Organization: Hitachi, Ltd., Japan
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1
MIME-Version: 1.0
To: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Re: Kprobes: pre-handler with interrupts enabled - is it possible?
References: <54EB4194.7040901@rosalab.ru> <54EBF464.7020704@hitachi.com> <54EC1487.4020902@rosalab.ru>
In-Reply-To: <54EC1487.4020902@rosalab.ru>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1797
Lines: 46

(2015/02/24 15:04), Eugene Shatokhin wrote:
> 24.02.2015 06:47, Masami Hiramatsu пишет:
>> No, that is not allowed. I mean, you can do anything you want to do
>> on your handler (enabling preemption/irq etc.) but the result may be
>> not safe (it can crash your kernel, but it's not a kprobes' bug).
> 
> Yes, that is why I am asking.
> 
>> Actually, enable interrupts on kprobe handlers can cause reentering
>> kprobes (by kprobes on interrupt handlers), and currently kprobe skips
>> all those reentered kprobes.
>> Is it acceptable that some of your kprobe handlers are not fired when
>> hitting?
> 
> I think, yes. When a software breakpoint hits, my system decodes the 
> instruction, finds the address that is about to be accessed and tries to 
> place a hardware breakpoint on that memory area.
> 
> There are only 4 hardware breakpoints a CPU can use on x86, so if the 
> software breakpoint hits too often, the system will not be able to 
> process all hits anyway because all HW breakpoints may be already in use.
> 
>> Would you mean sleep on your handler??
> 
> No, I use mdelay(). It is, in essence, a busy-wait loop as far as I 
> know. The delay intervals may vary, the default is 5 jiffies.

Hmm, here I couldn't understand. If mdelay() does busy-wait loop, why
would you like to enable irq??
Other code doesn't work on the core while waiting.

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/