Re: [patch 1/6] mmu_notifier: Core code

Andrea Arcangeli
2008-01-29T13:59:34Z

On Mon, Jan 28, 2008 at 12:28:41PM -0800, Christoph Lameter wrote:
> +struct mmu_notifier_head {
> + struct hlist_head head;
> +};
> +
> struct mm_struct {
> struct vm_area_struct * mmap; /* list of VMAs */
> struct rb_root mm_rb;
> @@ -219,6 +223,8 @@ struct mm_struct {
> /* aio bits */
> rwlock_t ioctx_list_lock;
> struct kioctx *ioctx_list;
> +
> + struct mmu_notifier_head mmu_notifier; /* MMU notifier list */
> };

Not sure why you prefer to waste ram when MMU_NOTIFIER=n, this is a
regression (a minor one though).

> + /*
> + * lock indicates that the function is called under spinlock.
> + */
> + void (*invalidate_range)(struct mmu_notifier *mn,
> + struct mm_struct *mm,
> + unsigned long start, unsigned long end,
> + int lock);
> +};

It's out of my reach how can you be ok with lock=1. You said you have
to block, if you can deal with lock=1 once, why can't you deal with
lock=1 _always_?

> +/*
> + * Note that all notifiers use RCU. The updates are only guaranteed to be
> + * visible to other processes after a RCU quiescent period!
> + */
> +void __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
> +{
> + hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier.head);
> +}
> +EXPORT_SYMBOL_GPL(__mmu_notifier_register);
> +
> +void mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
> +{
> + down_write(&mm->mmap_sem);
> + __mmu_notifier_register(mn, mm);
> + up_write(&mm->mmap_sem);
> +}
> +EXPORT_SYMBOL_GPL(mmu_notifier_register);

The down_write is garbage. The caller should put it around
mmu_notifier_register if something. The same way the caller should
call synchronize_rcu after mmu_notifier_register if it needs
synchronous behavior from the notifiers. The default version of
mmu_notifier_register shouldn't be cluttered with unnecessary locking.