Re: [PATCH 1/9] ftrace: Move the recursion testing into global headers

Miroslav Benes
2020-10-30T09:13:54Z

Hi,

> +static __always_inline int trace_get_context_bit(void)
> +{
> + int bit;
> +
> + if (in_interrupt()) {
> + if (in_nmi())
> + bit = 0;
> +
> + else if (in_irq())
> + bit = 1;
> + else
> + bit = 2;
> + } else
> + bit = 3;
> +
> + return bit;
> +}
> +
> +static __always_inline int trace_test_and_set_recursion(int start, int max)
> +{
> + unsigned int val = current->trace_recursion;
> + int bit;
> +
> + /* A previous recursion check was made */
> + if ((val & TRACE_CONTEXT_MASK) > max)
> + return 0;
> +
> + bit = trace_get_context_bit() + start;
> + if (unlikely(val & (1 << bit)))
> + return -1;
> +
> + val |= 1 << bit;
> + current->trace_recursion = val;
> + barrier();
> +
> + return bit;
> +}

how does this work in case of NMI? trace_get_context_bit() returns 0 (it
does not change later in the patch set). "start" in
trace_test_and_set_recursion() is 0 zero too as used later in the patch
set by ftrace_test_recursion_trylock(). So trace_test_and_set_recursion()
returns 0. That is perfectly sane, but then...

> +static __always_inline void trace_clear_recursion(int bit)
> +{
> + unsigned int val = current->trace_recursion;
> +
> + if (!bit)
> + return;

... the bit is not cleared here.

> + bit = 1 << bit;
> + val &= ~bit;
> +
> + barrier();
> + current->trace_recursion = val;
> +}

Thanks
Miroslav