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Date: Wed, 1 Aug 2012 16:01:21 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Roland McGrath <roland@hack.frob.com>, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org, ananth@in.ibm.com,
        a.p.zijlstra@chello.nl, mingo@redhat.com, srikar@linux.vnet.ibm.com
Subject: Re: Q: user_enable_single_step() && update_debugctlmsr()
Message-ID: <20120801140121.GA5333@redhat.com>
References: <20120730141638.GA5306@redhat.com> <1343735548-18101-1-git-send-email-bigeasy@linutronix.de> <1343735548-18101-2-git-send-email-bigeasy@linutronix.de> <20120731175108.GC14576@redhat.com> <50183273.9070304@linutronix.de> <20120801122616.GA32705@redhat.com> <20120801130118.GA2386@redhat.com> <50192FF5.1060208@linutronix.de> <20120801134652.GA4707@redhat.com> <50193528.3070503@linutronix.de>
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On 08/01, Sebastian Andrzej Siewior wrote:
>
> On 08/01/2012 03:46 PM, Oleg Nesterov wrote:
>
>>>> But, worse, isn't it wrong? Suppose that debugger switches to
>>>> another TIF_SINGLESTEP&&   !TIF_BLOCKSTEP task, in this case
>>>> we "leak" DEBUGCTLMSR_BTF, no?
>>>
>>> __switch_to_xtra() should notice the difference in the TIF_BLOCKSTEP
>>> flag and disable it.
>>
>> And how it can notice the difference if there is no difference?
>>
>> (unless, of course debugger is TIF_BLOCKSTEP'ed).
>
> Yes. enable_step() sets DEBUGCTLMSR_BTF along with TIF_BLOCKSTEP.
> kprobes checks the same flag before touching DEBUGCTLMSR_BTF.

It seems that you replied to the wrong email or I am confused ;)

Let's ignore kprobes here.

Oleg.