linux-kernel - [PATCH 2/2] drm/i915/gem: Use mmu_notifier_range_mayfail() to avoid waiting inside reclaim

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Message-Id: <20200624080248.3701-2-chris@chris-wilson.co.uk>
Date:   Wed, 24 Jun 2020 09:02:48 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>
Subject: [PATCH 2/2] drm/i915/gem: Use mmu_notifier_range_mayfail() to avoid waiting inside reclaim

The direct reclaim path may trigger the mmu_notifier callback as part of
try_to_unmap_one. As this is purely an opportunitistic attempt to
reclaim pages, and will be called from any allocation context under
unknown conditions (that include attempting to allocate pages for the
userptr object itself and subsequently trying to reclaim parts of the
partially acquired object) we have to be careful never to wait on
anything being held by the calling context. Since that is unknown, we
have to avoid waiting from inside direct reclaim.

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
---
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 9c53eb883400..72cfb91230ea 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -103,6 +103,7 @@ userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 	it = interval_tree_iter_first(&mn->objects, range->start, end);
 	while (it) {
 		struct drm_i915_gem_object *obj;
+		unsigned int flags;
 
 		if (!mmu_notifier_range_blockable(range)) {
 			ret = -EAGAIN;
@@ -126,9 +127,12 @@ userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 		}
 		spin_unlock(&mn->lock);
 
-		ret = i915_gem_object_unbind(obj,
-					     I915_GEM_OBJECT_UNBIND_ACTIVE |
-					     I915_GEM_OBJECT_UNBIND_BARRIER);
+		flags = (I915_GEM_OBJECT_UNBIND_ACTIVE |
+			 I915_GEM_OBJECT_UNBIND_BARRIER);
+		if (mmu_notifier_range_mayfail(range))
+			flags = 0;
+
+		ret = i915_gem_object_unbind(obj, flags);
 		if (ret == 0)
 			ret = __i915_gem_object_put_pages(obj);
 		i915_gem_object_put(obj);
-- 
2.20.1