Re: [PATCH 1/7] introduce atomic_dec_and_lock_irqsave()

[Oleg Nesterov]

On 08/30, Roman Zippel wrote:
> Hi,
> 
> On Wed, 30 Aug 2006, Oleg Nesterov wrote:
> 
> > > Why does this need protection against interrupts?
> > 
> > uidhash_lock can be taken from irq context. For example, delayed_put_task_struct()
> > does __put_task_struct()->free_uid().
> 
> AFAICT it's called via rcu, does that mean anything released via rcu has 
> to be protected against interrupts?

RCU means softirq, probably we can use spin_lock_bh() to protect against deadlock.
But free_uid() may be called with irqs disabled, we can't use local_bh_enable()
in such a case.

Oleg.

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