Re: [PATCH 2/3] mm: workingset: make shadow_lru_isolate() use locking suffix

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2018-06-24 22:57:53 [+0300], Vladimir Davydov wrote:
> On Fri, Jun 22, 2018 at 05:12:20PM +0200, Sebastian Andrzej Siewior wrote:
> > shadow_lru_isolate() disables interrupts and acquires a lock. It could
> > use spin_lock_irq() instead. It also uses local_irq_enable() while it
> > could use spin_unlock_irq()/xa_unlock_irq().
> > 
> > Use proper suffix for lock/unlock in order to enable/disable interrupts
> > during release/acquire of a lock.
> > 
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> I don't like when a spin lock is locked with local_irq_disabled +
> spin_lock and unlocked with spin_unlock_irq - it looks asymmetric.
> IMHO the code is pretty easy to follow as it is - local_irq_disable in
> scan_shadow_nodes matches local_irq_enable in shadow_lru_isolate.

it is not asymmetric because a later patch makes it use spin_lock_irq(),
too. If you use local_irq_disable() and a spin_lock() (like you suggest
in 3/3 as well) then you separate the locking instruction. It works as
expected on vanilla but break other locking implementations like those
on RT. Also if the locking changes then the local_irq_disable() part
will be forgotten like you saw in 1/3 of this series.

Sebastian