Re: [PATCH RFC] 'spinlock/rwlock fixes' V3 [1/1]

[Peter Chubb]

>>>>> "Chris" == Chris Wedgwood <cw@xxxxxxxx> writes:

Chris> On Wed, Jan 19, 2005 at 07:01:04PM -0800, Andrew Morton wrote:

Chris> It still isn't enough to rid of the rwlock_read_locked and
Chris> rwlock_write_locked usage in kernel/spinlock.c as those are
Chris> needed for the cpu_relax() calls so we have to decide on
Chris> suitable names still...  

I suggest reversing the sense of the macros, and having read_can_lock()
and write_can_lock()

Meaning:
	read_can_lock() --- a read_lock() would have succeeded
	write_can_lock() --- a write_lock() would have succeeded.

IA64 implementation:

#define read_can_lock(x)  (*(volatile int *)x >= 0)
#define write_can_lock(x) (*(volatile int *)x == 0)

Then use them as
     !read_can_lock(x)
where you want the old semantics.  The compiler ought to be smart
enough to optimise the boolean ops.

---
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
The technical we do immediately,  the political takes *forever*



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