On 2023/06/23 19:11, Sebastian Andrzej Siewior wrote:
> | unsigned __seqprop_spinlock_sequence(const seqcount_spinlock_t *s)
> | {
> | unsigned seq = READ_ONCE(s->seqcount.sequence);
> |
> | if (unlikely(seq & 1)) {
> | spin_lock(s->lock);
> | spin_unlock(s->lock);
> | seq = READ_ONCE(s->seqcount.sequence);
> | }
> | return seq;
> | }
OK. I understood that read_seqbegin() implies spin_lock()/spin_unlock() if RT.
What a deep macro. Thank you for explanation.
Well,
/*
* Zonelists may change due to hotplug during allocation. Detect when zonelists
* have been rebuilt so allocation retries. Reader side does not lock and
* retries the allocation if zonelist changes. Writer side is protected by the
* embedded spin_lock.
*/
is not accurate. Something like below?
If !RT, reader side does not lock and retries the allocation if zonelist changes.
If RT, reader side grabs and releases the embedded spin_lock in order to wait
for zonelist change operations to complete.
Hmm, I feel worried that kmalloc(GFP_ATOMIC) from hard IRQ context might sleep if RT...
