Re: [PATCH 1/7] mmu_notifier: add call_srcu and sync function for listener to delay call and sync.

[Oded Gabbay <oded.gabbay@amd.com>]

On 17/07/14 21:46, j.glisse@gmail.com wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> New mmu_notifier listener are eager to cleanup there structure after the
> mmu_notifier::release callback. In order to allow this the patch provide
> a function that allows to add a delayed call to the mmu_notifier srcu. It
> also add a function that will call barrier_srcu so those listener can sync
> with mmu_notifier.

Tested with amdkfd and iommuv2 driver
So,
Tested-by: Oded Gabbay <oded.gabbay@amd.com>
>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> ---
>   include/linux/mmu_notifier.h |  6 ++++++
>   mm/mmu_notifier.c            | 40 +++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index deca874..2728869 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -170,6 +170,8 @@ extern int __mmu_notifier_register(struct mmu_notifier *mn,
>   				   struct mm_struct *mm);
>   extern void mmu_notifier_unregister(struct mmu_notifier *mn,
>   				    struct mm_struct *mm);
> +extern void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
> +					       struct mm_struct *mm);
>   extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
>   extern void __mmu_notifier_release(struct mm_struct *mm);
>   extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
> @@ -288,6 +290,10 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
>   	set_pte_at(___mm, ___address, __ptep, ___pte);			\
>   })
>
> +extern void mmu_notifier_call_srcu(struct rcu_head *rcu,
> +				   void (*func)(struct rcu_head *rcu));
> +extern void mmu_notifier_synchronize(void);
> +
>   #else /* CONFIG_MMU_NOTIFIER */
>
>   static inline void mmu_notifier_release(struct mm_struct *mm)
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index 41cefdf..950813b 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -23,6 +23,25 @@
>   static struct srcu_struct srcu;
>
>   /*
> + * This function allows mmu_notifier::release callback to delay a call to
> + * a function that will free appropriate resources. The function must be
> + * quick and must not block.
> + */
> +void mmu_notifier_call_srcu(struct rcu_head *rcu,
> +			    void (*func)(struct rcu_head *rcu))
> +{
> +	call_srcu(&srcu, rcu, func);
> +}
> +EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
> +
> +void mmu_notifier_synchronize(void)
> +{
> +	/* Wait for any running method to finish. */
> +	srcu_barrier(&srcu);
> +}
> +EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
> +
> +/*
>    * This function can't run concurrently against mmu_notifier_register
>    * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
>    * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
> @@ -53,7 +72,6 @@ void __mmu_notifier_release(struct mm_struct *mm)
>   		 */
>   		if (mn->ops->release)
>   			mn->ops->release(mn, mm);
> -	srcu_read_unlock(&srcu, id);
>
>   	spin_lock(&mm->mmu_notifier_mm->lock);
>   	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
> @@ -69,6 +87,7 @@ void __mmu_notifier_release(struct mm_struct *mm)
>   		hlist_del_init_rcu(&mn->hlist);
>   	}
>   	spin_unlock(&mm->mmu_notifier_mm->lock);
> +	srcu_read_unlock(&srcu, id);
>
>   	/*
>   	 * synchronize_srcu here prevents mmu_notifier_release from returning to
> @@ -325,6 +344,25 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
>   }
>   EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
>
> +/*
> + * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
> + */
> +void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
> +					struct mm_struct *mm)
> +{
> +	spin_lock(&mm->mmu_notifier_mm->lock);
> +	/*
> +	 * Can not use list_del_rcu() since __mmu_notifier_release
> +	 * can delete it before we hold the lock.
> +	 */
> +	hlist_del_init_rcu(&mn->hlist);
> +	spin_unlock(&mm->mmu_notifier_mm->lock);
> +
> +	BUG_ON(atomic_read(&mm->mm_count) <= 0);
> +	mmdrop(mm);
> +}
> +EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
> +
>   static int __init mmu_notifier_init(void)
>   {
>   	return init_srcu_struct(&srcu);
>

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