On Thu, Oct 03, 2024 at 01:39:06PM +0200, Przemek Kitszel wrote:

Change scoped_guard() to make reasoning about it easier for static
analysis tools (smatch, compiler diagnostics), especially to enable them
to tell if the given scoped_guard() is conditional (interruptible-locks,
try-locks) or not (like simple mutex_lock()).

Add compile-time error if scoped_cond_guard() is used for non-conditional
lock class.

Beyond easier tooling and a little shrink reported by bloat-o-meter:
add/remove: 3/2 grow/shrink: 45/55 up/down: 1573/-2069 (-496)
this patch enables developer to write code like:

int foo(struct my_drv *adapter)
{
	scoped_guard(spinlock, &adapter->some_spinlock)
		return adapter->spinlock_protected_var;
}

Current scoped_guard() implementation does not support that,
due to compiler complaining:
error: control reaches end of non-void function [-Werror=return-type]

Technical stuff about the change:
scoped_guard() macro uses common idiom of using "for" statement to declare
a scoped variable. Unfortunately, current logic is too hard for compiler
diagnostics to be sure that there is exactly one loop step; fix that.

To make any loop so trivial that there is no above warning, it must not
depend on any non-const variable to tell if there are more steps. There is
no obvious solution for that in C, but one could use the compound
statement expression with "goto" jumping past the "loop", effectively
leaving only the subscope part of the loop semantics.

More impl details:
one more level of macro indirection is now needed to avoid duplicating
label names;
I didn't spot any other place that is using the
"for (...; goto label) if (0) label: break;" idiom, so it's not packed
for reuse, what makes actual macros code cleaner.

There was also a need to introduce const true/false variable per lock
class, it is used to aid compiler diagnostics reasoning about "exactly
1 step" loops (note that converting that to function would undo the whole
benefit).

...

+#define __scoped_guard_labeled(_label, _name, args...)			\
+	for (CLASS(_name, scope)(args);					\
+	     __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name);	\
+		     ({ goto _label; }))				\
+		if (0)							\
+		_label:							\
+			break;						\
+		else

I believe the following will folow more the style we use in the kernel:

#define __scoped_guard_labeled(_label, _name, args...)			\
	for (CLASS(_name, scope)(args);					\
	     __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name);	\
		     ({ goto _label; }))				\
		if (0) {						\
_label:									\
			break;						\
		} else

...

-	     *done = NULL; !done; done = (void *)1) \
+	     *done = NULL; !done; done = (void *)1 +  	\

You have TABs/spaces mix in this line now.

-- 
With Best Regards,
Andy Shevchenko