On Fri, Nov 25, 2016 at 12:23:56PM +0000, Mark Rutland wrote:
> Naming will be problematic; calling them ATOMIC_* makes tham sound like
> they work on atomic_t. That and I have no idea how to ensure correct
> usage tree-wide; I'm not sure if/how Coccinelle can help.
>
> Peter, thoughts?
Something like so perhaps?
---
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
#define WARN_SINGLE_COPY_ALIGNMENT(ptr) \
WARN_ON_ONCE(((unsigned long)(ptr)) & (sizeof(*(ptr))-1))
#else
#define WARN_SINGLE_COPY_ALIGNMENT(ptr)
#endif
/*
* Provide accessors for Single-Copy atomicy.
*
* That is, ensure that machine word sized loads/stores to naturally
* aligned variables are single instructions.
*
* By reason of not being able to use C11 atomic crud, use our beloved
* volatile qualifier. Since volatile tells the compiler the value can
* be changed behind its back, it must use Single-Copy atomic loads and
* stores to access them, otherwise it runs the risk of load/store
* tearing.
*/
#define SINGLE_LOAD(x) \
{( \
compiletime_assert_atomic_type(typeof(x)); \
WARN_SINGLE_COPY_ALIGNMENT(&(x)); \
READ_ONCE(x); \
})
#define SINGLE_STORE(x, v) \
({ \
compiletime_assert_atomic_type(typeof(x)); \
WARN_SINGLE_COPY_ALIGNMENT(&(x)); \
WRITE_ONCE(x, v); \
})
