Re: [LTP] [PATCH] powerpc: Fix hcall tracepoint recursion

Steven Rostedt
2010-10-22T14:14:28Z

On Thu, 2010-10-21 at 21:52 +1100, Anton Blanchard wrote:

> Anton
> --
>
> Subject: [PATCH] powerpc: Fix hcall tracepoint recursion
>
> Spinlocks on shared processor partitions use H_YIELD to notify the
> hypervisor we are waiting on another virtual CPU. Unfortunately this means
> the hcall tracepoints can recurse.
>
> The patch below adds a percpu depth and checks it on both the entry and
> exit hcall tracepoints.
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>
> Index: powerpc.git/arch/powerpc/platforms/pseries/lpar.c
> ===================================================================
> --- powerpc.git.orig/arch/powerpc/platforms/pseries/lpar.c 2010-10-21 17:32:00.980003644 +1100
> +++ powerpc.git/arch/powerpc/platforms/pseries/lpar.c 2010-10-21 17:34:54.942681273 +1100
> @@ -701,6 +701,13 @@ EXPORT_SYMBOL(arch_free_page);
> /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
> extern long hcall_tracepoint_refcount;
>
> +/*
> + * Since the tracing code might execute hcalls we need to guard against
> + * recursion. One example of this are spinlocks calling H_YIELD on
> + * shared processor partitions.
> + */
> +static DEFINE_PER_CPU(unsigned int, hcall_trace_depth);
> +
> void hcall_tracepoint_regfunc(void)
> {
> hcall_tracepoint_refcount++;
> @@ -713,12 +720,42 @@ void hcall_tracepoint_unregfunc(void)
>
> void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
> {
> + unsigned long flags;
> + unsigned int *depth;
> +
> + local_irq_save(flags);
> +
> + depth = &__get_cpu_var(hcall_trace_depth);
> +
> + if (*depth)
> + goto out;
> +
> + (*depth)++;
> trace_hcall_entry(opcode, args);
> + (*depth)--;
> +
> +out:
> + local_irq_restore(flags);
> }
>
> void __trace_hcall_exit(long opcode, unsigned long retval,
> unsigned long *retbuf)
> {
> + unsigned long flags;
> + unsigned int *depth;
> +
> + local_irq_save(flags);
> +
> + depth = &__get_cpu_var(hcall_trace_depth);
> +
> + if (*depth)
> + goto out;
> +
> + (*depth)++;
> trace_hcall_exit(opcode, retval, retbuf);
> + (*depth)--;
> +
> +out:
> + local_irq_restore(flags);
> }
> #endif

That's similar to the example that I wrote, but without the encapsulated
code and with disabling interrupts for the reasons you gave.

Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

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