mm, oom: distinguish blockable mode for mmu notifiers

There are several blockable mmu notifiers which might sleep in
mmu_notifier_invalidate_range_start and that is a problem for the
oom_reaper because it needs to guarantee a forward progress so it cannot
depend on any sleepable locks.

Currently we simply back off and mark an oom victim with blockable mmu
notifiers as done after a short sleep.  That can result in selecting a new
oom victim prematurely because the previous one still hasn't torn its
memory down yet.

We can do much better though.  Even if mmu notifiers use sleepable locks
there is no reason to automatically assume those locks are held.  Moreover
majority of notifiers only care about a portion of the address space and
there is absolutely zero reason to fail when we are unmapping an unrelated
range.  Many notifiers do really block and wait for HW which is harder to
handle and we have to bail out though.

This patch handles the low hanging fruit.
__mmu_notifier_invalidate_range_start gets a blockable flag and callbacks
are not allowed to sleep if the flag is set to false.  This is achieved by
using trylock instead of the sleepable lock for most callbacks and
continue as long as we do not block down the call chain.

I think we can improve that even further because there is a common pattern
to do a range lookup first and then do something about that.  The first
part can be done without a sleeping lock in most cases AFAICS.

The oom_reaper end then simply retries if there is at least one notifier
which couldn't make any progress in !blockable mode.  A retry loop is
already implemented to wait for the mmap_sem and this is basically the
same thing.

The simplest way for driver developers to test this code path is to wrap
userspace code which uses these notifiers into a memcg and set the hard
limit to hit the oom.  This can be done e.g.  after the test faults in all
the mmu notifier managed memory and set the hard limit to something really
small.  Then we are looking for a proper process tear down.

[akpm@linux-foundation.org: coding style fixes]
[akpm@linux-foundation.org: minor code simplification]
Link: http://lkml.kernel.org/r/20180716115058.5559-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Christian König <christian.koenig@amd.com> # AMD notifiers
Acked-by: Leon Romanovsky <leonro@mellanox.com> # mlx and umem_odp
Reported-by: David Rientjes <rientjes@google.com>
Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
Cc: Dennis Dalessandro <dennis.dalessandro@intel.com>
Cc: Sudeep Dutt <sudeep.dutt@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 64 insertions, 14 deletions

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
index a365ea2383d1..e55508b39496 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
@@ -178,12 +178,18 @@ void amdgpu_mn_unlock(struct amdgpu_mn *mn)
  *
  * @amn: our notifier
  */
-static void amdgpu_mn_read_lock(struct amdgpu_mn *amn)
+static int amdgpu_mn_read_lock(struct amdgpu_mn *amn, bool blockable)
 {
-	mutex_lock(&amn->read_lock);
+	if (blockable)
+		mutex_lock(&amn->read_lock);
+	else if (!mutex_trylock(&amn->read_lock))
+		return -EAGAIN;
+
 	if (atomic_inc_return(&amn->recursion) == 1)
 		down_read_non_owner(&amn->lock);
 	mutex_unlock(&amn->read_lock);
+
+	return 0;
 }
 
 /**
@@ -239,10 +245,11 @@ static void amdgpu_mn_invalidate_node(struct amdgpu_mn_node *node,
  * Block for operations on BOs to finish and mark pages as accessed and
  * potentially dirty.
  */
-static void amdgpu_mn_invalidate_range_start_gfx(struct mmu_notifier *mn,
+static int amdgpu_mn_invalidate_range_start_gfx(struct mmu_notifier *mn,
 						 struct mm_struct *mm,
 						 unsigned long start,
-						 unsigned long end)
+						 unsigned long end,
+						 bool blockable)
 {
 	struct amdgpu_mn *amn = container_of(mn, struct amdgpu_mn, mn);
 	struct interval_tree_node *it;
@@ -250,17 +257,28 @@ static void amdgpu_mn_invalidate_range_start_gfx(struct mmu_notifier *mn,
 	/* notification is exclusive, but interval is inclusive */
 	end -= 1;
 
-	amdgpu_mn_read_lock(amn);
+	/* TODO we should be able to split locking for interval tree and
+	 * amdgpu_mn_invalidate_node
+	 */
+	if (amdgpu_mn_read_lock(amn, blockable))
+		return -EAGAIN;
 
 	it = interval_tree_iter_first(&amn->objects, start, end);
 	while (it) {
 		struct amdgpu_mn_node *node;
 
+		if (!blockable) {
+			amdgpu_mn_read_unlock(amn);
+			return -EAGAIN;
+		}
+
 		node = container_of(it, struct amdgpu_mn_node, it);
 		it = interval_tree_iter_next(it, start, end);
 
 		amdgpu_mn_invalidate_node(node, start, end);
 	}
+
+	return 0;
 }
 
 /**
@@ -275,10 +293,11 @@ static void amdgpu_mn_invalidate_range_start_gfx(struct mmu_notifier *mn,
  * necessitates evicting all user-mode queues of the process. The BOs
  * are restorted in amdgpu_mn_invalidate_range_end_hsa.
  */
-static void amdgpu_mn_invalidate_range_start_hsa(struct mmu_notifier *mn,
+static int amdgpu_mn_invalidate_range_start_hsa(struct mmu_notifier *mn,
 						 struct mm_struct *mm,
 						 unsigned long start,
-						 unsigned long end)
+						 unsigned long end,
+						 bool blockable)
 {
 	struct amdgpu_mn *amn = container_of(mn, struct amdgpu_mn, mn);
 	struct interval_tree_node *it;
@@ -286,13 +305,19 @@ static void amdgpu_mn_invalidate_range_start_hsa(struct mmu_notifier *mn,
 	/* notification is exclusive, but interval is inclusive */
 	end -= 1;
 
-	amdgpu_mn_read_lock(amn);
+	if (amdgpu_mn_read_lock(amn, blockable))
+		return -EAGAIN;
 
 	it = interval_tree_iter_first(&amn->objects, start, end);
 	while (it) {
 		struct amdgpu_mn_node *node;
 		struct amdgpu_bo *bo;
 
+		if (!blockable) {
+			amdgpu_mn_read_unlock(amn);
+			return -EAGAIN;
+		}
+
 		node = container_of(it, struct amdgpu_mn_node, it);
 		it = interval_tree_iter_next(it, start, end);
 
@@ -304,6 +329,8 @@ static void amdgpu_mn_invalidate_range_start_hsa(struct mmu_notifier *mn,
 				amdgpu_amdkfd_evict_userptr(mem, mm);
 		}
 	}
+
+	return 0;
 }
 
 /**
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index dcd6e230d16a..2c9b284036d1 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -112,10 +112,11 @@ static void del_object(struct i915_mmu_object *mo)
 	mo->attached = false;
 }
 
-static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
+static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 						       struct mm_struct *mm,
 						       unsigned long start,
-						       unsigned long end)
+						       unsigned long end,
+						       bool blockable)
 {
 	struct i915_mmu_notifier *mn =
 		container_of(_mn, struct i915_mmu_notifier, mn);
@@ -124,7 +125,7 @@ static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 	LIST_HEAD(cancelled);
 
 	if (RB_EMPTY_ROOT(&mn->objects.rb_root))
-		return;
+		return 0;
 
 	/* interval ranges are inclusive, but invalidate range is exclusive */
 	end--;
@@ -132,6 +133,10 @@ static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 	spin_lock(&mn->lock);
 	it = interval_tree_iter_first(&mn->objects, start, end);
 	while (it) {
+		if (!blockable) {
+			spin_unlock(&mn->lock);
+			return -EAGAIN;
+		}
 		/* The mmu_object is released late when destroying the
 		 * GEM object so it is entirely possible to gain a
 		 * reference on an object in the process of being freed
@@ -154,6 +159,8 @@ static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 
 	if (!list_empty(&cancelled))
 		flush_workqueue(mn->wq);
+
+	return 0;
 }
 
 static const struct mmu_notifier_ops i915_gem_userptr_notifier = {
diff --git a/drivers/gpu/drm/radeon/radeon_mn.c b/drivers/gpu/drm/radeon/radeon_mn.c
index abd24975c9b1..f8b35df44c60 100644
--- a/drivers/gpu/drm/radeon/radeon_mn.c
+++ b/drivers/gpu/drm/radeon/radeon_mn.c
@@ -118,19 +118,27 @@ static void radeon_mn_release(struct mmu_notifier *mn,
  * We block for all BOs between start and end to be idle and
  * unmap them by move them into system domain again.
  */
-static void radeon_mn_invalidate_range_start(struct mmu_notifier *mn,
+static int radeon_mn_invalidate_range_start(struct mmu_notifier *mn,
 					     struct mm_struct *mm,
 					     unsigned long start,
-					     unsigned long end)
+					     unsigned long end,
+					     bool blockable)
 {
 	struct radeon_mn *rmn = container_of(mn, struct radeon_mn, mn);
 	struct ttm_operation_ctx ctx = { false, false };
 	struct interval_tree_node *it;
+	int ret = 0;
 
 	/* notification is exclusive, but interval is inclusive */
 	end -= 1;
 
-	mutex_lock(&rmn->lock);
+	/* TODO we should be able to split locking for interval tree and
+	 * the tear down.
+	 */
+	if (blockable)
+		mutex_lock(&rmn->lock);
+	else if (!mutex_trylock(&rmn->lock))
+		return -EAGAIN;
 
 	it = interval_tree_iter_first(&rmn->objects, start, end);
 	while (it) {
@@ -138,6 +146,11 @@ static void radeon_mn_invalidate_range_start(struct mmu_notifier *mn,
 		struct radeon_bo *bo;
 		long r;
 
+		if (!blockable) {
+			ret = -EAGAIN;
+			goto out_unlock;
+		}
+
 		node = container_of(it, struct radeon_mn_node, it);
 		it = interval_tree_iter_next(it, start, end);
 
@@ -166,7 +179,10 @@ static void radeon_mn_invalidate_range_start(struct mmu_notifier *mn,
 		}
 	}
 	
+out_unlock:
 	mutex_unlock(&rmn->lock);
+
+	return ret;
 }
 
 static const struct mmu_notifier_ops radeon_mn_ops = {