Re: [LTP] BUG: dead loop in PowerPC hcall tracepoint (Was: [PATCH v2] Add ftrace-stress-test to LTP)

Li Zefan
2010-10-19T00:49:09Z

Steven Rostedt wrote:
> On Mon, 2010-10-18 at 11:19 +0800, Li Zefan wrote:
>
>> This is a dead loop:
>>
>> trace_hcall_entry() -> trace_clock_global() -> trace_hcall_entry() ..
>>
>> And this is a PPC specific bug. Hope some ppc guys will fix it?
>> Or we kill trace_clock_global() if no one actually uses it..
>
> trace_clock_global() is used by many. I use it (and recommend using it)
> on boxes where the TSC is horribly out of sync, and the trace needs
> synchronization between CPUs.
>
> The trace_hcall_entry and exit has wrappers already. Just add recursion
> protection there.
>

Right, I thought of this. But as I have no machine to test, I'll leave
this to others.

> Perhaps something like this:
>
> (Not compiled nor ran)
>
> +static DEFINE_PER_CPU(hcall_trace_disable);
> +
> void hcall_tracepoint_regfunc(void)
> {
> hcall_tracepoint_refcount++;
> }
>
> void hcall_tracepoint_unregfunc(void)
> {
> hcall_tracepoint_refcount--;
> }
>
> +int __trace_disable_check(void)
> +{
> + if (!hcall_tracepoint_refcount)
> + return 1;
> +
> + if (get_cpu_var(hcall_trace_disable)) {
> + put_cpu_var(hcall_trace_disable);
> + return 1;
> + }
> +
> + __get_cpu_var(hcall_trace_disable)++;
> +
> + return 0;
> +}
> +
> +void __trace_disable_put(void)
> +{
> + __get_cpu_var(hcall_trace_disable)--;
> + put_cpu_var(hcall_trace_disable);
> +}
> +
> void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
> {
> + int trace_disable;
> +
> + if (__trace_disable_check())
> + return;
> +
> trace_hcall_entry(opcode, args);
> + __trace_disable_put();
> }
>
> void __trace_hcall_exit(long opcode, unsigned long retval,
> unsigned long *retbuf)
> {
> + if (__trace_disable_check())
> + return;
> +
> trace_hcall_exit(opcode, retval, retbuf);
> + __trace_disable_put();
> }
>
> -- Steve
>
>
>
>

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