[PATCH v3 2/2] drm/amdgpu: Fix lockdep false positive in amdgpu_lockdep_init

From: Vitaly Prosyak <[email protected]>

Move fs_reclaim_acquire() to before all lock acquisitions to eliminate
false positive circular locking dependency warning.

This is a 7.2-cycle regression fix suitable for stable backport.

v3: Address Mikhail Gavrilov technical review:
    - Clarify that fs_reclaim_acquire/release pair only REGISTERS the
      fs_reclaim lock class, does NOT create a static edge when called
      with no locks held
    - Explain that the actual fs_reclaim -> notifier_lock edge is
      established at runtime during memory reclaim -> MMU notifier path
    - Add Cc: Arunpravin PaneerSelvam

v2: Address Mikhail Gavrilov review feedback:
    - Fix author name: Michael -> Mikhail Gavrilov in all trailers
    - Add Fixes: tag to link regression to original commit
    - Add Tested-by: Mikhail Gavrilov (tested on RX 7900 XTX)

Fixes: 1d0f5838b126 ("drm/amdgpu: Add lockdep annotations for lock ordering validation")
Reported-by: Mikhail Gavrilov <[email protected]>
Analyzed-by: Mikhail Gavrilov <[email protected]>
Test-case-by: Mikhail Gavrilov <[email protected]>
Tested-by: Mikhail Gavrilov <[email protected]>
Suggested-by: Christian König <[email protected]>
Tested-by: Vitaly Prosyak <[email protected]>
Cc: Christian König <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Arunpravin PaneerSelvam <[email protected]>
Cc: [email protected]
Signed-off-by: Vitaly Prosyak <[email protected]>
Change-Id: I3f1a19877615cefc2e5d7c063144a6404a96ba38
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c
index b251350b1fb2..5f1f1960ef72 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_lockdep.c
@@ -151,6 +151,20 @@ int amdgpu_lockdep_init(void)
 	 * This establishes the dependency chain.
 	 */
 
+	/*
+	 * Register fs_reclaim lock class FIRST, before taking any locks.
+	 *
+	 * This acquire/release pair does NOT create a static lockdep edge
+	 * (no locks are held between acquire and release). It only registers
+	 * the fs_reclaim lock class with lockdep.
+	 *
+	 * The actual fs_reclaim -> notifier_lock dependency is established at
+	 * RUNTIME when memory reclaim invokes MMU notifiers:
+	 *   fs_reclaim (held by reclaim) -> notifier_lock (acquired in callback)
+	 */
+	fs_reclaim_acquire(GFP_KERNEL);
+	fs_reclaim_release(GFP_KERNEL);
+
 	/* Level 1: Global userq scheduler mutex (outermost) */
 	mutex_lock(&locks->userq_sch_mutex);
 
@@ -168,12 +182,6 @@ int amdgpu_lockdep_init(void)
 
 	/* Level 7: DRM file list mutex */
 	mutex_lock(&locks->filelist_mutex);
-	/*
-	 * Mark potential memory reclaim boundary.
-	 * GPU operations might trigger memory allocation/reclaim.
-	 */
-	fs_reclaim_acquire(GFP_KERNEL);
-
 	/* Level 8: SRBM register access */
 	mutex_lock(&locks->srbm_mutex);
 	/* Level 9: GRBM index access */
@@ -190,7 +198,6 @@ int amdgpu_lockdep_init(void)
 	spin_unlock_irqrestore(&locks->mmio_idx_lock, flags);
 	mutex_unlock(&locks->grbm_idx_mutex);
 	mutex_unlock(&locks->srbm_mutex);
-	fs_reclaim_release(GFP_KERNEL);
 
 	mutex_unlock(&locks->filelist_mutex);
 	mutex_unlock(&locks->reset_lock);
-- 
2.54.0