mm/hmm: HMM should have a callback before MM is destroyed

hmm_mirror_register() registers a callback for when the CPU pagetable is
modified.  Normally, the device driver will call hmm_mirror_unregister()
when the process using the device is finished.  However, if the process
exits uncleanly, the struct_mm can be destroyed with no warning to the
device driver.

Link: http://lkml.kernel.org/r/20180323005527.758-4-jglisse@redhat.com
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 36dd21f..fa7b51f 100644 (file)
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -218,6 +218,16 @@ enum hmm_update_type {
  * @update: callback to update range on a device
  */
 struct hmm_mirror_ops {
+       /* release() - release hmm_mirror
+        *
+        * @mirror: pointer to struct hmm_mirror
+        *
+        * This is called when the mm_struct is being released.
+        * The callback should make sure no references to the mirror occur
+        * after the callback returns.
+        */
+       void (*release)(struct hmm_mirror *mirror);
+
        /* sync_cpu_device_pagetables() - synchronize page tables
         *
         * @mirror: pointer to struct hmm_mirror

diff --git a/mm/hmm.c b/mm/hmm.c
index 320545b..8116727 100644 (file)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -160,6 +160,32 @@ static void hmm_invalidate_range(struct hmm *hmm,
        up_read(&hmm->mirrors_sem);
 }
 
+static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+       struct hmm_mirror *mirror;
+       struct hmm *hmm = mm->hmm;
+
+       down_write(&hmm->mirrors_sem);
+       mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
+                                         list);
+       while (mirror) {
+               list_del_init(&mirror->list);
+               if (mirror->ops->release) {
+                       /*
+                        * Drop mirrors_sem so callback can wait on any pending
+                        * work that might itself trigger mmu_notifier callback
+                        * and thus would deadlock with us.
+                        */
+                       up_write(&hmm->mirrors_sem);
+                       mirror->ops->release(mirror);
+                       down_write(&hmm->mirrors_sem);
+               }
+               mirror = list_first_entry_or_null(&hmm->mirrors,
+                                                 struct hmm_mirror, list);
+       }
+       up_write(&hmm->mirrors_sem);
+}
+
 static void hmm_invalidate_range_start(struct mmu_notifier *mn,
                                       struct mm_struct *mm,
                                       unsigned long start,
@@ -185,6 +211,7 @@ static void hmm_invalidate_range_end(struct mmu_notifier *mn,
 }
 
 static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
+       .release                = hmm_release,
        .invalidate_range_start = hmm_invalidate_range_start,
        .invalidate_range_end   = hmm_invalidate_range_end,
 };
@@ -230,7 +257,7 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
        struct hmm *hmm = mirror->hmm;
 
        down_write(&hmm->mirrors_sem);
-       list_del(&mirror->list);
+       list_del_init(&mirror->list);
        up_write(&hmm->mirrors_sem);
 }
 EXPORT_SYMBOL(hmm_mirror_unregister);