mm/mmu_notifiers: hoist do_mmu_notifier_register down_write to the caller

This simplifies the code to not have so many one line functions and extra
logic. __mmu_notifier_register() simply becomes the entry point to
register the notifier, and the other one calls it under lock.

Also add a lockdep_assert to check that the callers are holding the lock
as expected.

Link: https://lore.kernel.org/r/20190806231548.25242-2-jgg@ziepe.ca
Suggested-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index b567062..218a6f1 100644 (file)
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -236,22 +236,22 @@ void __mmu_notifier_invalidate_range(struct mm_struct *mm,
 }
 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
 
-static int do_mmu_notifier_register(struct mmu_notifier *mn,
-                                   struct mm_struct *mm,
-                                   int take_mmap_sem)
+/*
+ * Same as mmu_notifier_register but here the caller must hold the
+ * mmap_sem in write mode.
+ */
+int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 {
        struct mmu_notifier_mm *mmu_notifier_mm;
        int ret;
 
+       lockdep_assert_held_write(&mm->mmap_sem);
        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 
-       ret = -ENOMEM;
        mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
        if (unlikely(!mmu_notifier_mm))
-               goto out;
+               return -ENOMEM;
 
-       if (take_mmap_sem)
-               down_write(&mm->mmap_sem);
        ret = mm_take_all_locks(mm);
        if (unlikely(ret))
                goto out_clean;
@@ -279,13 +279,11 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
 
        mm_drop_all_locks(mm);
 out_clean:
-       if (take_mmap_sem)
-               up_write(&mm->mmap_sem);
        kfree(mmu_notifier_mm);
-out:
        BUG_ON(atomic_read(&mm->mm_users) <= 0);
        return ret;
 }
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 
 /*
  * Must not hold mmap_sem nor any other VM related lock when calling
@@ -302,19 +300,14 @@ out:
  */
 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 {
-       return do_mmu_notifier_register(mn, mm, 1);
-}
-EXPORT_SYMBOL_GPL(mmu_notifier_register);
+       int ret;
 
-/*
- * Same as mmu_notifier_register but here the caller must hold the
- * mmap_sem in write mode.
- */
-int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
-{
-       return do_mmu_notifier_register(mn, mm, 0);
+       down_write(&mm->mmap_sem);
+       ret = __mmu_notifier_register(mn, mm);
+       up_write(&mm->mmap_sem);
+       return ret;
 }
-EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
 
 /* this is called after the last mmu_notifier_unregister() returned */
 void __mmu_notifier_mm_destroy(struct mm_struct *mm)