[Intel-gfx] [PATCH 2/2] drm/i915/gt: Acquire ce->active before ce->pin_count/ce->pin_mutex

[Chris Wilson]

<0> [198.668822] gem_exec-1246    0.... 193899010us : timeline_advance: timeline_advance:387 GEM_BUG_ON(!atomic_read(&tl->pin_count))
<0> [198.668859] ---------------------------------
<4> [198.669619] ------------[ cut here ]------------
<2> [198.669621] kernel BUG at drivers/gpu/drm/i915/gt/intel_timeline.c:387!
<4> [198.669703] invalid opcode: 0000 [#1] PREEMPT SMP PTI
<4> [198.669712] CPU: 0 PID: 1246 Comm: gem_exec_create Tainted: G     U  W         5.5.0-rc6-CI-CI_DRM_7755+ #1
<4> [198.669723] Hardware name:  /NUC7i5BNB, BIOS BNKBL357.86A.0054.2017.1025.1822 10/25/2017
<4> [198.669776] RIP: 0010:timeline_advance+0x7b/0xe0 [i915]
<4> [198.669785] Code: 00 48 c7 c2 10 f1 46 a0 48 c7 c7 70 1b 32 a0 e8 bb dd e7 e0 bf 01 00 00 00 e8 d1 af e7 e0 31 f6 bf 09 00 00 00 e8 35 ef d8 e0 <0f> 0b 48 c7 c1 48 fa 49 a0 ba 84 01 00 00 48 c7 c6 10 f1 46 a0 48
<4> [198.669803] RSP: 0018:ffffc900004c3a38 EFLAGS: 00010296
<4> [198.669810] RAX: ffff888270b35140 RBX: ffff88826f32ee00 RCX: 0000000000000006
<4> [198.669818] RDX: 00000000000017c5 RSI: 0000000000000000 RDI: 0000000000000009
<4> [198.669826] RBP: ffffc900004c3a64 R08: 0000000000000000 R09: 0000000000000000
<4> [198.669834] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88826f9b5980
<4> [198.669841] R13: 0000000000000cc0 R14: ffffc900004c3dc0 R15: ffff888253610068
<4> [198.669849] FS:  00007f63e663fe40(0000) GS:ffff888276c00000(0000) knlGS:0000000000000000
<4> [198.669857] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4> [198.669864] CR2: 00007f171f8e39a8 CR3: 000000026b1f6005 CR4: 00000000003606f0
<4> [198.669872] Call Trace:
<4> [198.669924]  intel_timeline_get_seqno+0x12/0x40 [i915]
<4> [198.669977]  __i915_request_create+0x76/0x5a0 [i915]
<4> [198.670024]  i915_request_create+0x86/0x1c0 [i915]
<4> [198.670068]  i915_gem_do_execbuffer+0xbf2/0x2500 [i915]
<4> [198.670082]  ? __lock_acquire+0x460/0x15d0
<4> [198.670128]  i915_gem_execbuffer2_ioctl+0x11f/0x470 [i915]
<4> [198.670171]  ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]
<4> [198.670181]  drm_ioctl_kernel+0xa7/0xf0
<4> [198.670188]  drm_ioctl+0x2e1/0x390
<4> [198.670233]  ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]

Fixes: 841350223816 ("drm/i915/gt: Drop mutex serialisation between context pin/unpin")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_context.c | 46 ++++++++++++++-----------
 drivers/gpu/drm/i915/i915_active.h      |  6 ++++
 2 files changed, 31 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 23137b2a8689..57e8a051ddc2 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -67,21 +67,18 @@ static int intel_context_active_acquire(struct intel_context *ce)
 {
 	int err;
 
-	err = i915_active_acquire(&ce->active);
-	if (err)
-		return err;
+	__i915_active_acquire(&ce->active);
+
+	if (intel_context_is_barrier(ce))
+		return 0;
 
 	/* Preallocate tracking nodes */
-	if (!intel_context_is_barrier(ce)) {
-		err = i915_active_acquire_preallocate_barrier(&ce->active,
-							      ce->engine);
-		if (err) {
-			i915_active_release(&ce->active);
-			return err;
-		}
-	}
+	err = i915_active_acquire_preallocate_barrier(&ce->active,
+						      ce->engine);
+	if (err)
+		i915_active_release(&ce->active);
 
-	return 0;
+	return err;
 }
 
 static void intel_context_active_release(struct intel_context *ce)
@@ -101,13 +98,19 @@ int __intel_context_do_pin(struct intel_context *ce)
 			return err;
 	}
 
-	if (mutex_lock_interruptible(&ce->pin_mutex))
-		return -EINTR;
+	err = i915_active_acquire(&ce->active);
+	if (err)
+		return err;
+
+	if (mutex_lock_interruptible(&ce->pin_mutex)) {
+		err = -EINTR;
+		goto out_release;
+	}
 
-	if (likely(!atomic_read(&ce->pin_count))) {
+	if (likely(!atomic_add_unless(&ce->pin_count, 1, 0))) {
 		err = intel_context_active_acquire(ce);
 		if (unlikely(err))
-			goto err;
+			goto out_unlock;
 
 		err = ce->ops->pin(ce);
 		if (unlikely(err))
@@ -117,18 +120,19 @@ int __intel_context_do_pin(struct intel_context *ce)
 			 ce->ring->head, ce->ring->tail);
 
 		smp_mb__before_atomic(); /* flush pin before it is visible */
+		atomic_inc(&ce->pin_count);
 	}
 
-	atomic_inc(&ce->pin_count);
 	GEM_BUG_ON(!intel_context_is_pinned(ce)); /* no overflow! */
-
-	mutex_unlock(&ce->pin_mutex);
-	return 0;
+	GEM_BUG_ON(i915_active_is_idle(&ce->active));
+	goto out_unlock;
 
 err_active:
 	intel_context_active_release(ce);
-err:
+out_unlock:
 	mutex_unlock(&ce->pin_mutex);
+out_release:
+	i915_active_release(&ce->active);
 	return err;
 }
 
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index b571f675c795..51e1e854ca55 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -188,6 +188,12 @@ int i915_active_acquire(struct i915_active *ref);
 bool i915_active_acquire_if_busy(struct i915_active *ref);
 void i915_active_release(struct i915_active *ref);
 
+static inline void __i915_active_acquire(struct i915_active *ref)
+{
+	GEM_BUG_ON(!atomic_read(&ref->count));
+	atomic_inc(&ref->count);
+}
+
 static inline bool
 i915_active_is_idle(const struct i915_active *ref)
 {
-- 
2.25.0