linux-kernel - x86: A process doesn't stop on hw breakpoints sometimes

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Message-ID: <CANaxB-xwu3pJmRDHDwRAug4Hz_XF9GSkOhZn-FCfsk_BiZL-xg@mail.gmail.com>
Date:	Mon, 23 May 2016 16:05:47 -0700
From:	Andrei Vagin <avagin@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: x86: A process doesn't stop on hw breakpoints sometimes

Hi,

We use breakpoints on CRIU to stop a processes before calling
rt_sigreturn and we found that sometimes a process runs through a
break-point without stopping on it.

https://github.com/xemul/criu/issues/162

A small reproducer is attached. It forks a child, stops it, sets a
breakpoint, executes a child, waits when it stops on the breakpoint. I
execute it a few times concurrently and wait a few minutes.

https://asciinema.org/a/006l3u5v82ubbkfy9fto07agd

I know that it can be reproduced on:
AMD A10 Micro-6700T
Intel(R) Core(TM) i5-5200U CPU @ 2.20GHz
Intel(R) Core(TM) i7-4600U CPU @ 2.10GHz

so It doesn't look like a bug in a processor.

Thanks,
Andrew

View attachment "bp3.c" of type "text/x-csrc" (2457 bytes)