mm/mmu_notifier: define the header pre-processor parts even if disabled

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.

Link: https://lore.kernel.org/r/20191112202231.3856-2-jgg@ziepe.ca
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 7fde88695f35..367670cfd02b 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -28,6 +28,19 @@ 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
  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers