[PATCH 4/4] mm, notifier: Catch sleeping/blocking for !blockable

[Daniel Vetter]

We need to make sure implementations don't cheat and don't have a
possible schedule/blocking point deeply burried where review can't
catch it.

I'm not sure whether this is the best way to make sure all the
might_sleep() callsites trigger, and it's a bit ugly in the code flow.
But it gets the job done.

Inspired by an i915 patch series which did exactly that, because the
rules haven't been entirely clear to us.

v2: Use the shiny new non_block_start/end annotations instead of
abusing preempt_disable/enable.

v3: Rebase on top of Glisse's arg rework.

v4: Rebase on top of more Glisse rework.

Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: "Christian KÃnig" <christian.koenig@xxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Reviewed-by: Christian KÃnig <christian.koenig@xxxxxxx>
Reviewed-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
 mm/mmu_notifier.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 538d3bb87f9b..856636d06ee0 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -181,7 +181,13 @@ int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
 	id = srcu_read_lock(&srcu);
 	hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
 		if (mn->ops->invalidate_range_start) {
-			int _ret = mn->ops->invalidate_range_start(mn, range);
+			int _ret;
+
+			if (!mmu_notifier_range_blockable(range))
+				non_block_start();
+			_ret = mn->ops->invalidate_range_start(mn, range);
+			if (!mmu_notifier_range_blockable(range))
+				non_block_end();
 			if (_ret) {
 				pr_info("%pS callback failed with %d in %sblockable context.\n",
 					mn->ops->invalidate_range_start, _ret,
-- 
2.23.0.rc1