Re: [PATCH] atomic: cleanup asm-generic atomic*.h inclusion

From: Arun Sharma
Date: Fri Jun 17 2011 - 14:41:27 EST

On 6/17/11 11:06 AM, Mike Frysinger wrote:

fixes one thing while breaking another. linux/atomic.h includes
asm/atomic.h which includes asm-generic/atomic.h which includes
asm-generic/atomic-long.h which needs atomic_add_unless(), but that
isnt provided until after the asm/atomic.h include in linux/atomic.h.

but linux/atomic.h needs asm/atomic.h before atomic_add_unless()
because it relies on the new __atomic_add_unless().

Right. I think we need to get rid of that include as well:

--- a/include/asm-generic/atomic.h
+++ b/include/asm-generic/atomic.h
@@ -156,7 +145,5 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)
#define smp_mb__before_atomic_inc() barrier()
#define smp_mb__after_atomic_inc() barrier()

-#include <asm-generic/atomic-long.h>
#endif /* __KERNEL__ */
#endif /* __ASM_GENERIC_ATOMIC_H */

since <linux/atomic.h> includes it directly now.

having linux/atomic.h and asm-generic/atomic.h just strikes me as
wrong. the point of asm-generic is to unify things, but now we have
two places to unify things without 0 indication as to which is for
which ? i'm wondering if we shouldnt convert all arches to
asm-generic/atomic.h and then add your new logic there and just skip
this whole linux/atomic.h mess.

I believe the logic is:

<asm-generic/atomic.h> shared code for simple archs that don't want to define their own primitives. Only used by 4 archs.

<linux/atomic.h> a header file that's usable in machine independent kernel code.

<linux/atomic.h> seems to be relatively recent, introduced by:

commit 3f9d35b9514da6757ca98831372518f9eeb71b33
Author: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Thu Nov 11 14:05:08 2010 -0800

atomic: add atomic_inc_not_zero_hint()

<asm-generic/atomic.h> came from:

commit d3cb487149bd706aa6aeb02042332a450978dc1c
Author: Christoph Lameter <clameter@xxxxxxxxxxxx>
Date: Fri Jan 6 00:11:20 2006 -0800

[PATCH] atomic_long_t & include/asm-generic/atomic.h V2

My guess is that if <linux/atomic.h> existed in 2006, people would've added shared code over there. Also, the code in <asm-generic/atomic.h> is not truly generic:

smp_mb__before_atomic_dec() for eg is implemented differently for some archs.

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