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

From: jglisse
Date: Wed Mar 21 2018 - 21:29:01 EST


From: Ralph Campbell <rcampbell@xxxxxxxxxx>

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 <rcampbell@xxxxxxxxxx>
Signed-off-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Evgeny Baskakov <ebaskakov@xxxxxxxxxx>
Cc: Mark Hairgrove <mhairgrove@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
---
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..34c16297f65e 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