Re: [PATCH] powerpc/xmon: Fix data-breakpoint

[Ravi Bangoria]

Hi Michael,

Can you please pull this patch.

Thanks,
Ravi

On Tuesday 22 November 2016 02:55 PM, Ravi Bangoria wrote:
> 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 
> ---
>  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);
>
>   /*

Re: [PATCH] powerpc/xmon: Fix data-breakpoint

[Ravi Bangoria]

Thanks Michael,

On Tuesday 22 November 2016 05:03 PM, Michael Ellerman wrote:
> Ravi Bangoria  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
>

Re: [PATCH] powerpc/xmon: Fix data-breakpoint

[Michael Ellerman]

Ravi Bangoria  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

[PATCH] powerpc/xmon: Fix data-breakpoint

[Ravi Bangoria]

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 
---
 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