mm/hmm: Remove racy protection against double-unregistration

No other register/unregister kernel API attempts to provide this kind of
protection as it is inherently racy, so just drop it.

Callers should provide their own protection, and it appears nouveau
already does.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Philip Yang <Philip.Yang@amd.com>

diff --git a/mm/hmm.c b/mm/hmm.c
index 6f5dc6d..2ef14b2 100644 (file)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -276,17 +276,11 @@ EXPORT_SYMBOL(hmm_mirror_register);
  */
 void hmm_mirror_unregister(struct hmm_mirror *mirror)
 {
-       struct hmm *hmm = READ_ONCE(mirror->hmm);
-
-       if (hmm == NULL)
-               return;
+       struct hmm *hmm = mirror->hmm;
 
        down_write(&hmm->mirrors_sem);
        list_del_init(&mirror->list);
-       /* To protect us against double unregister ... */
-       mirror->hmm = NULL;
        up_write(&hmm->mirrors_sem);
-
        hmm_put(hmm);
 }
 EXPORT_SYMBOL(hmm_mirror_unregister);