Re: [patch 1/4] mmu_notifier: Core code

Robin Holt
2008-01-25T18:39:56Z

> +#define mmu_notifier(function, mm, args...) \
...
> + if (__mn->ops->function) \
> + __mn->ops->function(__mn, \
> + mm, \
> + args); \

__mn->ops->function(__mn, mm, args); \
I realize it is a minor nit, but since we put the continuation in column
81 in the next define, can we do the same here and make this more
readable?

> + rcu_read_unlock(); \
...
> +#define mmu_rmap_notifier(function, args...) \
> + do { \
> + struct mmu_rmap_notifier *__mrn; \
> + struct hlist_node *__n; \
> + \

> +void mmu_notifier_release(struct mm_struct *mm)
> +{
> + struct mmu_notifier *mn;
> + struct hlist_node *n;
> +
> + if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) {
> + rcu_read_lock();
> + hlist_for_each_entry_rcu(mn, n,
> + &mm->mmu_notifier.head, hlist) {
> + if (mn->ops->release)
> + mn->ops->release(mn, mm);
> + hlist_del(&mn->hlist);

I think the hlist_del needs to be before the function callout so we can free
the structure without a use-after-free issue.

hlist_for_each_entry_rcu(mn, n,
&mm->mmu_notifier.head, hlist) {
hlist_del_rcu(&mn->hlist);
if (mn->ops->release)
mn->ops->release(mn, mm);

> +static DEFINE_SPINLOCK(mmu_notifier_list_lock);

Remove

> +
> +void mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
> +{
> + spin_lock(&mmu_notifier_list_lock);

Shouldn't this really be protected by the down_write(mmap_sem)? Maybe:
BUG_ON(!rwsem_is_write_locked(&mm->mmap_sem));

> + hlist_add_head(&mn->hlist, &mm->mmu_notifier.head);
hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier.head);

> + spin_unlock(&mmu_notifier_list_lock);
> +}
> +EXPORT_SYMBOL_GPL(mmu_notifier_register);
> +
> +void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
> +{
> + spin_lock(&mmu_notifier_list_lock);
> + hlist_del(&mn->hlist);

hlist_del_rcu? Ditto on the lock.

> + spin_unlock(&mmu_notifier_list_lock);
> +}
> +EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
> +
> +HLIST_HEAD(mmu_rmap_notifier_list);

static DEFINE_SPINLOCK(mmu_rmap_notifier_list_lock);

> +
> +void mmu_rmap_notifier_register(struct mmu_rmap_notifier *mrn)
> +{
> + spin_lock(&mmu_notifier_list_lock);
> + hlist_add_head_rcu(&mrn->hlist, &mmu_rmap_notifier_list);
> + spin_unlock(&mmu_notifier_list_lock);

spin_lock(&mmu_rmap_notifier_list_lock);
hlist_add_head_rcu(&mrn->hlist, &mmu_rmap_notifier_list);
spin_unlock(&mmu_rmap_notifier_list_lock);

> +}
> +EXPORT_SYMBOL(mmu_rmap_notifier_register);
> +
> +void mmu_rmap_notifier_unregister(struct mmu_rmap_notifier *mrn)
> +{
> + spin_lock(&mmu_notifier_list_lock);
> + hlist_del_rcu(&mrn->hlist);
> + spin_unlock(&mmu_notifier_list_lock);

spin_lock(&mmu_rmap_notifier_list_lock);
hlist_del_rcu(&mrn->hlist);
spin_unlock(&mmu_rmap_notifier_list_lock);

> @@ -2043,6 +2044,7 @@ void exit_mmap(struct mm_struct *mm)
> vm_unacct_memory(nr_accounted);
> free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
> tlb_finish_mmu(tlb, 0, end);
> + mmu_notifier_release(mm);

Can we consider moving this notifier or introducing an additional notifier
in the release or a flag to this one indicating early/late.

The GRU that Jack is concerned with would benefit from the early in
that it could just invalidate the GRU context and immediately all GRU
TLB entries are invalid. I believe Jack would like to also be able to
remove his entry from the mmu_notifier list in an effort to avoid the
page and range callouts.

XPMEM, would also benefit from a call early. We could make all the
segments as being torn down and start the recalls. We already have
this code in and working (have since it was first written 6 years ago).
In this case, all segments are torn down with a single message to each
of the importing partitions. In contrast, the teardown code which would
happen now would be one set of messages for each vma.

Thanks,
Robin