Subject: Re: [PATCH] powerpc/xmon: Fix data-breakpoint
To: Michael Ellerman <mpe@ellerman.id.au>
References: <1479806759-5409-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com>
 <87eg23vjds.fsf@concordia.ellerman.id.au>
Cc: benh@kernel.crashing.org, paulus@samba.org, npiggin@gmail.com,
        peterz@infradead.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, naveen.n.rao@linux.vnet.ibm.com,
        Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
From: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Date: Tue, 22 Nov 2016 17:20:38 +0530
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Thanks Michael,

On Tuesday 22 November 2016 05:03 PM, Michael Ellerman wrote:
> Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> writes:
>
>> Xmon data-breakpoint feature is broken.
>>
>> Whenever there is a watchpoint match occurs, hw_breakpoint_handler will
>> be called by do_break via notifier chains mechanism. If watchpoint is
>> registered by xmon, hw_breakpoint_handler won't find any associated
>> perf_event and returns immediately with NOTIFY_STOP. Similarly, do_break
>> also returns without notifying to xmon.
>>
>> Solve this by returning NOTIFY_DONE when hw_breakpoint_handler does not
>> find any perf_event associated with matched watchpoint.
> .. rather than NOTIFY_STOP, which tells the core code to continue
> calling the other breakpoint handlers including the xmon one.
>
> Right?

Yes.

> Also any idea when we broke this?

Hmm, not sure exactly. The code is same since it was merged in 2010 when
support for hw_breakpoint was added for server processor.

-Ravi

> cheers
>