[PATCH] drm/amdgpu: do not enter fs_reclaim under notifier_lock in lockdep training

[Mikhail Gavrilov]

amdgpu_lockdep_init() trains lockdep on the driver lock ordering by
taking a chain of dummy locks in order and calling fs_reclaim_acquire()
in the middle of it. The fs_reclaim_acquire()/fs_reclaim_release() pair
is placed while notifier_lock (amdgpu_notifier_lock_key) is held, which
teaches lockdep that it is legal to enter memory reclaim with the MMU
notifier lock held:

  notifier_lock -> vram_lock -> reset_domain->sem -> reset_lock ->
  fs_reclaim

notifier_lock is, however, acquired from the MMU notifier invalidate
callback amdgpu_hmm_invalidate_gfx(), which mm/ runs from inside memory
reclaim via __mmu_notifier_invalidate_range_start(). That establishes
the mandatory reverse ordering:

  fs_reclaim -> mmu_notifier_invalidate_range_start -> notifier_lock

The two together form a cycle. It stays dormant until reclaim first
unmaps a page covered by an amdgpu userptr interval notifier, at which
point kswapd closes the loop and lockdep reports a false circular
locking dependency:

  WARNING: possible circular locking dependency detected
  kswapd0/268 is trying to acquire lock:
   (&amdgpu_notifier_lock_key){+.+.}, at: amdgpu_hmm_invalidate_gfx
  but task is already holding lock:
   (mmu_notifier_invalidate_range_start){+.+.}, at: try_to_unmap_one

A lock that is taken inside an MMU notifier callback must never be held
across a reclaiming allocation, so the fs_reclaim annotation does not
belong inside the notifier_lock region. Drop it. The remaining chain
still teaches the intended lock nesting.

Fixes: 1d0f5838b126 ("drm/amdgpu: Add lockdep annotations for lock ordering validation")
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c
index d5d71fd7c70d..eeb3b5007f80 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c
@@ -150,12 +150,6 @@ int amdgpu_lockdep_init(void)
 	/* Level 6: Reset control lock */
 	mutex_lock(&reset_ctl.reset_lock);
 
-	/*
-	 * Mark potential memory reclaim boundary.
-	 * GPU operations might trigger memory allocation/reclaim.
-	 */
-	fs_reclaim_acquire(GFP_KERNEL);
-
 	/* Level 7: SRBM register access */
 	mutex_lock(&srbm_mutex);
 
@@ -175,8 +169,6 @@ int amdgpu_lockdep_init(void)
 	mutex_unlock(&grbm_idx_mutex);
 	mutex_unlock(&srbm_mutex);
 
-	fs_reclaim_release(GFP_KERNEL);
-
 	mutex_unlock(&reset_ctl.reset_lock);
 	up_read(&reset_domain->sem);
 	mutex_unlock(&vram_lock);
-- 
2.54.0