Re: [PATCH for-next] RDMA/cma: Replace RMW with atomic bit-ops

[Stefan Metzmacher <metze@samba.org>]

Hi Håkon,

> +#define BIT_ACCESS_FUNCTIONS(b)							\
> +	static inline void set_##b(unsigned long flags)				\
> +	{									\
> +		/* set_bit() does not imply a memory barrier */			\
> +		smp_mb__before_atomic();					\
> +		set_bit(b, &flags);						\
> +		/* set_bit() does not imply a memory barrier */			\
> +		smp_mb__after_atomic();						\
> +	}									\

Don't you need to pass flags by reference to the inline function?
As far as I can see set_bit() operates on a temporary variable.

In order to check if inline functions are special I wrote this little check:

$ cat inline_arg.c
#include <stdio.h>

static inline void func(unsigned s, unsigned *p)
{
        printf("&s=%p p=%p\n", &s, p);
}

int main(void)
{
        unsigned flags = 0;

        func(flags, &flags);
        return 0;
}

$ gcc -O0 -o inline_arg inline_arg.c
$ ./inline_arg
&s=0x7ffd3a71616c p=0x7ffd3a716184

$ gcc -O6 -o inline_arg inline_arg.c
$ ./inline_arg
&s=0x7ffd87781064 p=0x7ffd87781060

It means s doesn't magically become 'flags' of the caller...

I'm I missing something?

metze