[zfs-code] Read-write locks in libzpool

[Ricardo Correia]

Hi,

I think I found a bug in the rw_enter() implementation (emulation?) in 
libzpool, file /usr/src/lib/libzpool/common/kernel.c:

void
rw_enter(krwlock_t *rwlp, krw_t rw)
{
        ASSERT(!RW_LOCK_HELD(rwlp));
        ASSERT(rwlp->rw_owner != (void *)-1UL);
        ASSERT(rwlp->rw_owner != curthread);

        if (rw == RW_READER)
                (void) rw_rdlock(&rwlp->rw_lock);
        else
                (void) rw_wrlock(&rwlp->rw_lock);

        rwlp->rw_owner = curthread;
}

Doesn't RW_LOCK_HELD() check if there's a reader or a writer locked? If it 
does, then these read-write locks would produce an assertion when multiple 
readers tried to lock it.

However, RW_LOCK_HELD() is being applied to "rwlp" instead 
of "&rwlp->rw_lock", which could explain why it's not failing.

Am I understanding this correctly?

Unfortunately POSIX threads don't have an equivalent of rw_lock_held(), 
rw_write_held(), mutex_held(), ..., so I really have to understand this in 
order to somehow emulate their behavior.

Thanks!