[PATCH v4 01/26] mm/mmu_notifiers: pass private data down to alloc_notifier()

[Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>]

The new allocation scheme introduced by 2c7933f53f6b ("mm/mmu_notifiers:
add a get/put scheme for the registration") provides a convenient way
for users to attach notifier data to an mm. However, it would be even
better to create this notifier data atomically.

Since the alloc_notifier() callback only takes an mm argument at the
moment, some users have to perform the allocation in two times.
alloc_notifier() initially creates an incomplete structure, which is
then finalized using more context once mmu_notifier_get() returns. This
second step requires carrying an initialization lock in the notifier
data and playing dirty tricks to order memory accesses against live
invalidation.

To simplify MMU notifier allocation, pass an allocation context to
mmu_notifier_get().

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Dimitri Sivanich <sivanich@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
---
 drivers/misc/sgi-gru/grutlbpurge.c |  4 ++--
 include/linux/mmu_notifier.h       | 10 ++++++----
 mm/mmu_notifier.c                  |  6 ++++--
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/misc/sgi-gru/grutlbpurge.c b/drivers/misc/sgi-gru/grutlbpurge.c
index 10921cd2608d..77610e1704f6 100644
--- a/drivers/misc/sgi-gru/grutlbpurge.c
+++ b/drivers/misc/sgi-gru/grutlbpurge.c
@@ -235,7 +235,7 @@ static void gru_invalidate_range_end(struct mmu_notifier *mn,
 		gms, range->start, range->end);
 }
 
-static struct mmu_notifier *gru_alloc_notifier(struct mm_struct *mm)
+static struct mmu_notifier *gru_alloc_notifier(struct mm_struct *mm, void *privdata)
 {
 	struct gru_mm_struct *gms;
 
@@ -266,7 +266,7 @@ struct gru_mm_struct *gru_register_mmu_notifier(void)
 {
 	struct mmu_notifier *mn;
 
-	mn = mmu_notifier_get_locked(&gru_mmuops, current->mm);
+	mn = mmu_notifier_get_locked(&gru_mmuops, current->mm, NULL);
 	if (IS_ERR(mn))
 		return ERR_CAST(mn);
 
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 736f6918335e..06e68fa2b019 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -207,7 +207,7 @@ struct mmu_notifier_ops {
 	 * callbacks are currently running. It is called from a SRCU callback
 	 * and cannot sleep.
 	 */
-	struct mmu_notifier *(*alloc_notifier)(struct mm_struct *mm);
+	struct mmu_notifier *(*alloc_notifier)(struct mm_struct *mm, void *privdata);
 	void (*free_notifier)(struct mmu_notifier *subscription);
 };
 
@@ -271,14 +271,16 @@ static inline 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);
+					     struct mm_struct *mm,
+					     void *privdata);
 static inline struct mmu_notifier *
-mmu_notifier_get(const struct mmu_notifier_ops *ops, struct mm_struct *mm)
+mmu_notifier_get(const struct mmu_notifier_ops *ops, struct mm_struct *mm,
+		 void *privdata)
 {
 	struct mmu_notifier *ret;
 
 	down_write(&mm->mmap_sem);
-	ret = mmu_notifier_get_locked(ops, mm);
+	ret = mmu_notifier_get_locked(ops, mm, privdata);
 	up_write(&mm->mmap_sem);
 	return ret;
 }
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index ef3973a5d34a..8beb9dcbe0fd 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -734,6 +734,7 @@ find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
  *                           the mm & ops
  * @ops: The operations struct being subscribe with
  * @mm : The mm to attach notifiers too
+ * @privdata: Initialization data passed down to ops->alloc_notifier()
  *
  * This function either allocates a new mmu_notifier via
  * ops->alloc_notifier(), or returns an already existing notifier on the
@@ -747,7 +748,8 @@ find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
  * and can be converted to an active mm pointer via mmget_not_zero().
  */
 struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
-					     struct mm_struct *mm)
+					     struct mm_struct *mm,
+					     void *privdata)
 {
 	struct mmu_notifier *subscription;
 	int ret;
@@ -760,7 +762,7 @@ struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
 			return subscription;
 	}
 
-	subscription = ops->alloc_notifier(mm);
+	subscription = ops->alloc_notifier(mm, privdata);
 	if (IS_ERR(subscription))
 		return subscription;
 	subscription->ops = ops;
-- 
2.25.0