On 2022-08-23 19:04:00 [+0200], Vlastimil Babka wrote: > The PREEMPT_RT specific disabling of irqs in __cmpxchg_double_slab() > (through slab_[un]lock()) is unnecessary as bit_spin_lock() disables > preemption and that's sufficient on RT where interrupts are threaded. maybe something like "… sufficient on PREEMPT_RT where no allocation/ free operation is performed in hardirq context and so interrupt the current operation." > That means we no longer need the slab_[un]lock() wrappers, so delete > them and rename the current __slab_[un]lock() to slab_[un]lock(). > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -454,7 +454,7 @@ static __always_inline void __slab_lock(struct slab *slab) … > /* > * Interrupts must be disabled (for the fallback code to work right), typically > - * by an _irqsave() lock variant. Except on PREEMPT_RT where locks are different > - * so we disable interrupts as part of slab_[un]lock(). > + * by an _irqsave() lock variant. Except on PREEMPT_RT where these variants do > + * not actually disable interrupts. On the other hand the migrate_disable() > + * done by bit_spin_lock() is sufficient on PREEMPT_RT thanks to its threaded > + * interrupts. " On PREEMPT_RT the preempt_disable(), which is part of bit_spin_lock(), is sufficient because the policy is not to allow any allocation/ free operation in hardirq context. Therefore nothing can interrupt the operation." This also includes SMP function calls (IPI). > */ > static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab, > void *freelist_old, unsigned long counters_old, Sebastian
