On Tue, 3 Nov 2020 15:10:43 +0100
Petr Mladek [off-list ref] wrote:

BTW: What is actually the purpose of paranoid_test, please?

It prevents nested ftrace_record_recursion() calls on the same CPU
(recursion, nesting from IRQ, NMI context).

Parallel calls from different CPUs are still possible:

CPU0					CPU1
if (!atomic_read(&paranoid_test))	if (!atomic_read(&paranoid_test))
   // passes				  // passes
   atomic_inc(&paranoid_test);            atomic_inc(&paranoid_test);


I do not see how a nested call could cause crash while a parallel
one would be OK.

Yeah, I should make that per cpu, but was lazy. ;-)

It was added at the end.

I'll update that to a per cpu, and local inc operations.

-- Steve