Re: [Xen-devel] [PATCH v2 01/15] mm/mmu_notifier: define the header pre-processor parts even if disabled

[John Hubbard <jhubbard@xxxxxxxxxx>]

On 10/28/19 1:10 PM, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> 
> Now that we have KERNEL_HEADER_TEST all headers are generally compile
> tested, so relying on makefile tricks to avoid compiling code that depends
> on CONFIG_MMU_NOTIFIER is more annoying.
> 
> Instead follow the usual pattern and provide most of the header with only
> the functions stubbed out when CONFIG_MMU_NOTIFIER is disabled. This
> ensures code compiles no matter what the config setting is.
> 
> While here, struct mmu_notifier_mm is private to mmu_notifier.c, move it.

and correct a minor spelling error in a comment. Good. :)

> 
> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> ---
>  include/linux/mmu_notifier.h | 46 +++++++++++++-----------------------
>  mm/mmu_notifier.c            | 13 ++++++++++
>  2 files changed, 30 insertions(+), 29 deletions(-)
> 

Because this is correct as-is, you can add:

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>


...whether or not you take the following recommendation, which is:
you've only done part of the job of making struct mmu_notifier_mm 
private to mmu_notifier.c. There's more:

* struct mmu_notifier_mm is referred to in two places now: mm_types.h
  and (still) mmu_notifier.h. Therefore:

    a) Move the last two traces of it out of mmu_notifier.h, and

    b) Put a forward declaration in mm_types.h, which is where it
       belongs because that's where it's referred to.

So if you apply this incremental patch on top, I think it's where
you want to be:

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 2222fa795284..df93a3cc0da9 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -25,6 +25,7 @@
 
 struct address_space;
 struct mem_cgroup;
+struct mmu_notifier_mm;
 
 /*
  * Each physical page in the system has a struct page associated with
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 51b92ba013dd..84efd2c51f5c 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -8,7 +8,6 @@
 #include <linux/srcu.h>
 #include <linux/interval_tree.h>
 
-struct mmu_notifier_mm;
 struct mmu_notifier;
 struct mmu_notifier_range;
 struct mmu_range_notifier;
@@ -263,10 +262,7 @@ struct mmu_notifier_range {
        enum mmu_notifier_event event;
 };
 
-static inline int mm_has_notifiers(struct mm_struct *mm)
-{
-       return unlikely(mm->mmu_notifier_mm);
-}
+int mm_has_notifiers(struct mm_struct *mm);
 
 struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops 
*ops,
                                             struct mm_struct *mm);
@@ -477,10 +473,7 @@ static inline void mmu_notifier_invalidate_range(struct 
mm_struct *mm,
                __mmu_notifier_invalidate_range(mm, start, end);
 }
 
-static inline void mmu_notifier_mm_init(struct mm_struct *mm)
-{
-       mm->mmu_notifier_mm = NULL;
-}
+void mmu_notifier_mm_init(struct mm_struct *mm);
 
 static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
 {
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 2b7485919ecf..107f9406a92d 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -47,6 +47,16 @@ struct mmu_notifier_mm {
        struct hlist_head deferred_list;
 };
 
+int mm_has_notifiers(struct mm_struct *mm)
+{
+       return unlikely(mm->mmu_notifier_mm);
+}
+
+void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+       mm->mmu_notifier_mm = NULL;
+}
+
 /*
  * This is a collision-retry read-side/write-side 'lock', a lot like a
  * seqcount, however this allows multiple write-sides to hold it at


thanks,

John Hubbard
NVIDIA

> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index 1bd8e6a09a3c27..12bd603d318ce7 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -7,8 +7,9 @@
>  #include <linux/mm_types.h>
>  #include <linux/srcu.h>
>  
> +struct mmu_notifier_mm;
>  struct mmu_notifier;
> -struct mmu_notifier_ops;
> +struct mmu_notifier_range;
>  
>  /**
>   * enum mmu_notifier_event - reason for the mmu notifier callback
> @@ -40,36 +41,8 @@ enum mmu_notifier_event {
>       MMU_NOTIFY_SOFT_DIRTY,
>  };
>  
> -#ifdef CONFIG_MMU_NOTIFIER
> -
> -#ifdef CONFIG_LOCKDEP
> -extern struct lockdep_map __mmu_notifier_invalidate_range_start_map;
> -#endif
> -
> -/*
> - * The mmu notifier_mm structure is allocated and installed in
> - * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
> - * critical section and it's released only when mm_count reaches zero
> - * in mmdrop().
> - */
> -struct mmu_notifier_mm {
> -     /* all mmu notifiers registerd in this mm are queued in this list */
> -     struct hlist_head list;
> -     /* to serialize the list modifications and hlist_unhashed */
> -     spinlock_t lock;
> -};
> -
>  #define MMU_NOTIFIER_RANGE_BLOCKABLE (1 << 0)
>  
> -struct mmu_notifier_range {
> -     struct vm_area_struct *vma;
> -     struct mm_struct *mm;
> -     unsigned long start;
> -     unsigned long end;
> -     unsigned flags;
> -     enum mmu_notifier_event event;
> -};
> -
>  struct mmu_notifier_ops {
>       /*
>        * Called either by mmu_notifier_unregister or when the mm is
> @@ -249,6 +222,21 @@ struct mmu_notifier {
>       unsigned int users;
>  };
>  
> +#ifdef CONFIG_MMU_NOTIFIER
> +
> +#ifdef CONFIG_LOCKDEP
> +extern struct lockdep_map __mmu_notifier_invalidate_range_start_map;
> +#endif
> +
> +struct mmu_notifier_range {
> +     struct vm_area_struct *vma;
> +     struct mm_struct *mm;
> +     unsigned long start;
> +     unsigned long end;
> +     unsigned flags;
> +     enum mmu_notifier_event event;
> +};
> +
>  static inline int mm_has_notifiers(struct mm_struct *mm)
>  {
>       return unlikely(mm->mmu_notifier_mm);
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index 7fde88695f35d6..367670cfd02b7b 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -27,6 +27,19 @@ struct lockdep_map 
> __mmu_notifier_invalidate_range_start_map = {
>  };
>  #endif
>  
> +/*
> + * The mmu notifier_mm structure is allocated and installed in
> + * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
> + * critical section and it's released only when mm_count reaches zero
> + * in mmdrop().
> + */
> +struct mmu_notifier_mm {
> +     /* all mmu notifiers registered in this mm are queued in this list */
> +     struct hlist_head list;
> +     /* to serialize the list modifications and hlist_unhashed */
> +     spinlock_t lock;
> +};
> +
>  /*
>   * This function can't run concurrently against mmu_notifier_register
>   * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
> 

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