Messages in this thread | | | Date | Thu, 24 Aug 2006 18:13:51 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/6] BC: beancounters core (API) |
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On 08/23, Andrew Morton wrote: > > On Wed, 23 Aug 2006 15:03:07 +0400 > Kirill Korotaev <dev@sw.ru> wrote: > > > +void __put_beancounter(struct beancounter *bc) > > +{ > > + unsigned long flags; > > + > > + /* equivalent to atomic_dec_and_lock_irqsave() */ > > + local_irq_save(flags); > > + if (likely(!atomic_dec_and_lock(&bc->bc_refcount, &bc_hash_lock))) { > > + local_irq_restore(flags); > > + if (unlikely(atomic_read(&bc->bc_refcount) < 0)) > > + printk(KERN_ERR "BC: Bad refcount: bc=%p, " > > + "luid=%d, ref=%d\n", > > + bc, bc->bc_id, > > + atomic_read(&bc->bc_refcount)); > > + return; > > + } > > + > > + BUG_ON(bc == &init_bc); > > + verify_held(bc); > > + hlist_del(&bc->hash); > > + spin_unlock_irqrestore(&bc_hash_lock, flags); > > + kmem_cache_free(bc_cachep, bc); > > +} > > I wonder if it's safe and worthwhile to optimise away the local_irq_save():
Suppose ->bc_refcount == 1
> if (atomic_dec_and_test(&bc->bc_refcount)) {
Yes, preempted or blocks on spin_lock() below.
another cpu locks bc_hash_lock, does get_beancounter() (beancounter_findcreate), then does put_beancounter(), and frees it.
> spin_lock_irqsave(&bc_hash_lock, flags); > if (atomic_read(&bc->bc_refcount) == 0) {
Yes,
> free it >
Already freed.
Oleg.
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