[PATCH 4/4] powerpc/pseries: warn if recursing into the hcall tracing code

[Naveen N. Rao]

Nicholas Piggin wrote:
> ---
>  arch/powerpc/platforms/pseries/lpar.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
> index 835e7f661a05..a961a7ebeab3 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -1828,8 +1828,11 @@ void hcall_tracepoint_unregfunc(void)
> 
>  /*
>   * Since the tracing code might execute hcalls we need to guard against
> - * recursion. H_CONFER from spin locks must be treated separately though
> - * and use _notrace plpar_hcall variants, see yield_to_preempted().
> + * recursion, but this always seems risky -- __trace_hcall_entry might be
> + * ftraced, for example. So warn in this case.

__trace_hcall_[entry|exit] aren't traced anymore since they now have the 
'notrace' annotation.

> + *
> + * H_CONFER from spin locks must be treated separately though and use _notrace
> + * plpar_hcall variants, see yield_to_preempted().
>   */
>  static DEFINE_PER_CPU(unsigned int, hcall_trace_depth);
> 
> @@ -1843,7 +1846,7 @@ notrace void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
> 
>  	depth = this_cpu_ptr(&hcall_trace_depth);
> 
> -	if (*depth)
> +	if (WARN_ON_ONCE(*depth))
>  		goto out;

I don't think this will be helpful. The hcall trace depth tracking is 
for the tracepoint and I suspect that this warning will be triggered 
quite easily. Since we have recursion protection, I don't think we 
should warn here.


- Naveen