Nathan Lynch [off-list ref] writes:

Michael Ellerman [off-list ref] writes:

quoted

Nathan Lynch via B4 Relay [off-list ref]
writes:

quoted

From: Nathan Lynch <redacted>

On RTAS platforms there is a general restriction that the OS must not
enter RTAS on more than one CPU at a time. This low-level
serialization requirement is satisfied by holding a spin
lock (rtas_lock) across most RTAS function invocations.

...

quoted

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 1fc0b3fffdd1..52f2242d0c28 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c

@@ -581,6 +652,28 @@ static const struct rtas_function *rtas_token_to_function(s32 token)
 	return NULL;
 }
 
+static void __rtas_function_lock(struct rtas_function *func)
+{
+	if (func && func->lock)
+		mutex_lock(func->lock);
+}

This is obviously going to defeat most static analysis tools.

I guess it's not that obvious to me :-) Is it because the mutex_lock()
is conditional? I'll improve this if it's possible.

Well maybe I'm not giving modern static analysis tools enough credit :)

But what I mean that it's not easy to reason about what the function
does in isolation. ie. all you can say is that it may or may not lock a
mutex, and you can't say which mutex.

quoted

I assume lockdep is OK with it though?

Seems to be, yes.

OK.

cheers