From: Daniel Vetter <daniel.vetter@ffwll.ch>
Date: Mon, 26 Aug 2019 22:14:24 +0200
Subject: mm, notifier: Catch sleeping/blocking for !blockable
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Patch-mainline: v5.4-rc1
Git-commit: ba170f76b69d1d45a60eaa9ec920c8fddd4c16f3
References: jsc#SLE-15176, jsc#SLE-16387

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.

Link: https://lore.kernel.org/r/20190826201425.17547-5-daniel.vetter@ffwll.ch
Reviewed-by: Christian König <christian.koenig@amd.com> (v1)
Reviewed-by: Jérôme Glisse <jglisse@redhat.com> (v4)
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 mm/mmu_notifier.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -168,7 +168,13 @@ int __mmu_notifier_invalidate_range_star
 	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,
@@ -210,8 +216,13 @@ void __mmu_notifier_invalidate_range_end
 			mn->ops->invalidate_range(mn, range->mm,
 						  range->start,
 						  range->end);
-		if (mn->ops->invalidate_range_end)
+		if (mn->ops->invalidate_range_end) {
+			if (!mmu_notifier_range_blockable(range))
+				non_block_start();
 			mn->ops->invalidate_range_end(mn, range);
+			if (!mmu_notifier_range_blockable(range))
+				non_block_end();
+		}
 	}
 	srcu_read_unlock(&srcu, id);
 	lock_map_release(&__mmu_notifier_invalidate_range_start_map);