On 6/6/19 11:44 AM, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
>
> So long a a struct hmm pointer exists, so should the struct mm it is
> linked too. Hold the mmgrab() as soon as a hmm is created, and mmdrop() it
> once the hmm refcount goes to zero.
>
> Since mmdrop() (ie a 0 kref on struct mm) is now impossible with a !NULL
> mm->hmm delete the hmm_hmm_destroy().
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> ---
> v2:
> - Fix error unwind paths in hmm_get_or_create (Jerome/Jason)
> ---
> include/linux/hmm.h | 3 ---
> kernel/fork.c | 1 -
> mm/hmm.c | 22 ++++------------------
> 3 files changed, 4 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 2d519797cb134a..4ee3acabe5ed22 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -586,14 +586,11 @@ static inline int hmm_vma_fault(struct hmm_mirror *mirror,
> }
>
> /* Below are for HMM internal use only! Not to be used by device driver! */
> -void hmm_mm_destroy(struct mm_struct *mm);
> -
> static inline void hmm_mm_init(struct mm_struct *mm)
> {
> mm->hmm = NULL;
> }
> #else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
> -static inline void hmm_mm_destroy(struct mm_struct *mm) {}
> static inline void hmm_mm_init(struct mm_struct *mm) {}
> #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index b2b87d450b80b5..588c768ae72451 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -673,7 +673,6 @@ void __mmdrop(struct mm_struct *mm)
> WARN_ON_ONCE(mm == current->active_mm);
> mm_free_pgd(mm);
> destroy_context(mm);
> - hmm_mm_destroy(mm);
This is particularly welcome, not to have an "HMM is special" case
in such a core part of process/mm code.
> mmu_notifier_mm_destroy(mm);
> check_mm(mm);
> put_user_ns(mm->user_ns);
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 8796447299023c..cc7c26fda3300e 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -29,6 +29,7 @@
> #include <linux/swapops.h>
> #include <linux/hugetlb.h>
> #include <linux/memremap.h>
> +#include <linux/sched/mm.h>
> #include <linux/jump_label.h>
> #include <linux/dma-mapping.h>
> #include <linux/mmu_notifier.h>
> @@ -82,6 +83,7 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm)
> hmm->notifiers = 0;
> hmm->dead = false;
> hmm->mm = mm;
> + mmgrab(hmm->mm);
>
> spin_lock(&mm->page_table_lock);
> if (!mm->hmm)
> @@ -109,6 +111,7 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm)
> mm->hmm = NULL;
> spin_unlock(&mm->page_table_lock);
> error:
> + mmdrop(hmm->mm);
> kfree(hmm);
> return NULL;
> }
> @@ -130,6 +133,7 @@ static void hmm_free(struct kref *kref)
> mm->hmm = NULL;
> spin_unlock(&mm->page_table_lock);
>
> + mmdrop(hmm->mm);
> mmu_notifier_call_srcu(&hmm->rcu, hmm_free_rcu);
> }
>
> @@ -138,24 +142,6 @@ static inline void hmm_put(struct hmm *hmm)
> kref_put(&hmm->kref, hmm_free);
> }
>
> -void hmm_mm_destroy(struct mm_struct *mm)
> -{
> - struct hmm *hmm;
> -
> - spin_lock(&mm->page_table_lock);
> - hmm = mm_get_hmm(mm);
> - mm->hmm = NULL;
> - if (hmm) {
> - hmm->mm = NULL;
> - hmm->dead = true;
> - spin_unlock(&mm->page_table_lock);
> - hmm_put(hmm);
> - return;
> - }
> -
> - spin_unlock(&mm->page_table_lock);
> -}
> -
> static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
> {
> struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
>
Failed to find any problems with this. :)
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
thanks,
--
John Hubbard
NVIDIA
