[PATCH 03/15] mm/hmm: HMM should have a callback before MM is destroyed v3

[jglisse]

From: Ralph Campbell <rcampb...@nvidia.com>

The hmm_mirror_register() function 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.

Changed since v1:
  - dropped VM_BUG_ON()
  - cc stable
Changed since v2:
  - drop stable
  - Split list removale and call to driver release callback. This
    allow the release callback to wait on any pending fault handler
    without deadlock.

Signed-off-by: Ralph Campbell <rcampb...@nvidia.com>
Signed-off-by: Jérôme Glisse <jgli...@redhat.com>
Reviewed-by: John Hubbard <jhubb...@nvidia.com>
Cc: Evgeny Baskakov <ebaska...@nvidia.com>
Cc: Mark Hairgrove <mhairgr...@nvidia.com>
---
 include/linux/hmm.h | 10 ++++++++++
 mm/hmm.c            | 29 ++++++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 36dd21fe5caf..fa7b51f65905 100644
--- 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 320545b98ff5..8116727766f7 100644
--- 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);
-- 
2.14.3