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[PATCH] powerpc/xmon: Fix data-breakpoint

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  [PATCH] powerpc/xmon: Fix data-breakpoint Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> - 2016-11-22 10:30 +0100
    Re: [PATCH] powerpc/xmon: Fix data-breakpoint Michael Ellerman <mpe@ellerman.id.au> - 2016-11-22 12:40 +0100
      Re: [PATCH] powerpc/xmon: Fix data-breakpoint Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> - 2016-11-22 13:00 +0100

#1527328 — [PATCH] powerpc/xmon: Fix data-breakpoint

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.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/hw_breakpoint.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 03d089b..469d86d 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -228,8 +228,10 @@ int hw_breakpoint_handler(struct die_args *args)
 	rcu_read_lock();
 
 	bp = __this_cpu_read(bp_per_reg);
-	if (!bp)
+	if (!bp) {
+		rc = NOTIFY_DONE;
 		goto out;
+	}
 	info = counter_arch_bp(bp);
 
 	/*
-- 
1.8.3.1

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#1527436

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?

Also any idea when we broke this?

cheers

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#1527444

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
>

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