On Fri, Sep 22, 2006 at 04:48:13PM +0900, Paul Mundt wrote:
> This might be a stupid question, but why exactly are we ripping out
> generic__raw_read_trylock() if architectures are going to implement a
> generic implementation anyways, rather than just changing it to match
> the proper semantics?
Because there is no generic definition of struct spinlock.
> int __lockfunc generic__raw_read_trylock(raw_rwlock_t *lock)
> {
> - __raw_read_lock(lock);
> - return 1;
> + atomic_t *count = (atomic_t *)lock;
> + atomic_dec(count);
> + if (atomic_read(count) >= 0)
> + return 1;
> + atomic_inc(count);
> + return 0;
> }
You're assuming:
- a spinlock is an atomic_t.
- Said atomic_t uses RW_LOCK_BIAS to indicate locked/unlocked.
This is true for m32r, but not for sparc. SuperH looks completely
broken -- I don't see how holding a read lock prevents someone else from
getting a write lock. The SH write_trylock uses RW_LOCK_BIAS, but
write_lock doesn't. Are there any SMP SH machines?
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