Re: [PATCH RFC V1] mm: convert rcu_read_lock() to srcu_read_lock(), thus allowing to sleep in callbacks

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

sagig@mellanox.com wrote:
> Now that anon_vma lock and i_mmap_mutex are both sleepable mutex, it is possible to schedule inside invalidation callbacks
> (such as invalidate_page, invalidate_range_start/end and change_pte) .
> This is essential for a scheduling HW sync in RDMA drivers which apply on demand paging methods.
>
> Signed-off-by: sagi grimberg<sagig@mellanox.co.il>

Ok, this is better, but it still does not work =)
Nobody synchronize with this srcu. There at least two candidates:
mmu_notifier_release() and mmu_notifier_unregister().
They call synchronize_rcu(), you must replace it with synchronize_srcu().

> ---
>   changes from V0:
>   1. srcu_struct should be shared and not allocated in each callback - removed from callbacks
>   2. added srcu_struct under mmu_notifier_mm
>   3. init_srcu_struct when creating mmu_notifier_mm
>   4. srcu_cleanup when destroying mmu_notifier_mm
>

> @@ -204,6 +208,8 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
>
>   	if (!mm_has_notifiers(mm)) {
>   		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
> +		if (init_srcu_struct(&mmu_notifier_mm->srcu))
> +			goto out_cleanup;

move it upper, out of mm->mmap_sem lock. and fix error path.


>   		spin_lock_init(&mmu_notifier_mm->lock);
>   		mm->mmu_notifier_mm = mmu_notifier_mm;
>   		mmu_notifier_mm = NULL;
> @@ -266,6 +272,7 @@ EXPORT_SYMBOL_GPL(__mmu_notifier_register);
>   void __mmu_notifier_mm_destroy(struct mm_struct *mm)
>   {
>   	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
> +	cleanup_srcu_struct(&mm->mmu_notifier_mm->srcu);
>   	kfree(mm->mmu_notifier_mm);
>   	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
>   }

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