On Tue, 11 Dec 2018, Jerome Glisse wrote:
> > > > The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
> > > > does not evaluate all its arguments, leading to a warning in one case:
> > > >
> > > > mm/migrate.c: In function 'migrate_vma_pages':
> > > > mm/migrate.c:2711:20: error: unused variable 'mm'
> > > > [-Werror=unused-variable]
> > > > struct mm_struct *mm = vma->vm_mm;
> > > >
> > > > Pass down the 'mm' as into the inline function as well so gcc can
> > > > see why the variable exists.
> > > >
> > > > Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for
> > > > invalidate_range_start/end calls v2")
> > >
> > > What about changing migrate.c (i actualy tried to do that everywhere in
> > > the patchset but i missed that spot) So we avoid one useless variable on
> > > such configuration:
> > >
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index f02bb4b22c1a..883fce631f47 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -2701,7 +2701,6 @@ static void migrate_vma_pages(struct migrate_vma
> > > *migrate)
> > > const unsigned long npages = migrate->npages;
> > > const unsigned long start = migrate->start;
> > > struct vm_area_struct *vma = migrate->vma;
> > > - struct mm_struct *mm = vma->vm_mm;
> > > struct mmu_notifier_range range;
> > > unsigned long addr, i;
> > > bool notified = false;
> > > @@ -2724,8 +2723,8 @@ static void migrate_vma_pages(struct migrate_vma
> > > *migrate)
> > > if (!notified) {
> > > notified = true;
> > >
> > > - mmu_notifier_range_init(&range, mm, addr,
> > > - migrate->end,
> > > + mmu_notifier_range_init(&range, vma->vm_mm,
> > > + addr, migrate->end,
> > > MMU_NOTIFY_CLEAR);
> > > mmu_notifier_invalidate_range_start(&range);
> > > }
> >
> > Wouldn't it be better to just declare mmu_notifier_range_init() as a
> > static inline function rather than a #define to avoid this warning?
>
> The define trick is use to drop the event parameter so that we do not
> need to define the event value for CONFIG_MMU_NOTIFIER=n case.
>
Hmm, strange that Arnd's build failure is only reporting about an unused
variable instead of MMU_NOTIFY_CLEAR being undefined :/
I think this should be done so that anybody using
mmu_notifier_range_init() doesn't need to worry about the implications of
*any* unused formal parameter as a result of how the #define is formed:
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -10,21 +10,6 @@
struct mmu_notifier;
struct mmu_notifier_ops;
-#ifdef CONFIG_MMU_NOTIFIER
-
-/*
- * 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;
-};
-
/**
* enum mmu_notifier_event - reason for the mmu notifier callback
* @MMU_NOTIFY_UNMAP: either munmap() that unmap the range or a mremap() that
@@ -53,6 +38,21 @@ enum mmu_notifier_event {
MMU_NOTIFY_SOFT_DIRTY,
};
+#ifdef CONFIG_MMU_NOTIFIER
+
+/*
+ * 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;
+};
+
struct mmu_notifier_range {
struct mm_struct *mm;
unsigned long start;
@@ -483,9 +483,14 @@ static inline void _mmu_notifier_range_init(struct
mmu_notifier_range *range,
range->end = end;
}
-#define mmu_notifier_range_init(range, mm, start, end, event) \
- _mmu_notifier_range_init(range, start, end)
-
+static inline void mmu_notifier_range_init(struct mmu_notifier_range *range,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end,
+ enum mmu_notifier_event event)
+{
+ _mmu_notifier_range_init(range, start, end);
+}
static inline int mm_has_notifiers(struct mm_struct *mm)
{
