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Date:   Wed, 14 Aug 2019 16:42:08 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Yann COLLETTE <ycollette.nospam@free.fr>
Cc:     linux-rt-users@vger.kernel.org
Subject: Re: Kernel 5.0.21rt16 hangs
Message-ID: <20190814144207.qi7qtcpvyfpoc7cj@linutronix.de>
References: <f410b429-db86-f81c-7c67-f563fa808b62@free.fr>
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On 2019-08-09 17:45:13 [+0200], Yann COLLETTE wrote:
> Hello,
Hi,

> I am using kernel-rt 5.0.21rt16 on fedora 30.

…
> Aug  9 17:16:35 localhost kernel: Preemption disabled at:
> Aug  9 17:16:35 localhost kernel: [<ffffffff8c67239e>]
> reservation_object_add_shared_fence+0x3e/0x1b0
> Aug  9 17:16:35 localhost kernel: CPU: 3 PID: 1087 Comm: Xorg Not tainted
> 5.0.21-rt16.fc30.x86_64 #1
> Aug  9 17:16:35 localhost kernel: Hardware name: HP 450-a121nf/2B29, BIOS
> A0.11 01/15/2016
> Aug  9 17:16:35 localhost kernel: Call Trace:
> Aug  9 17:16:35 localhost kernel: dump_stack+0x5c/0x80
> Aug  9 17:16:35 localhost kernel: ?
> reservation_object_add_shared_fence+0x3e/0x1b0
> Aug  9 17:16:35 localhost kernel: __schedule_bug.cold+0x44/0x51
> Aug  9 17:16:35 localhost kernel: __schedule+0x5c6/0x6f0
> Aug  9 17:16:35 localhost kernel: schedule+0x43/0xd0
> Aug  9 17:16:35 localhost kernel: rt_spin_lock_slowlock_locked+0x114/0x2b0
> Aug  9 17:16:35 localhost kernel: rt_spin_lock_slowlock+0x51/0x80
> Aug  9 17:16:35 localhost kernel: __wake_up_common_lock+0x61/0xb0
> Aug  9 17:16:35 localhost kernel: radeon_fence_is_signaled+0x74/0x90
> [radeon]
> Aug  9 17:16:35 localhost kernel:
> reservation_object_add_shared_fence+0x97/0x1b0
> Aug  9 17:16:35 localhost kernel: radeon_vm_bo_update+0x409/0x640 [radeon]
> Aug  9 17:16:35 localhost kernel: radeon_gem_va_ioctl+0x41c/0x500 [radeon]
…
> I don't know if this bug is related to the kernel of if this is a mesa
> problem.

That backtrace is kernel related. I'm not sure if this is related to the
hang up you observe.
Could you please try the following patch:


diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index bf4d4c80fbc67..c6370dcdd77d2 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -168,7 +168,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 		return 0;
 
 retry:
-	seq = read_seqcount_begin(&resv->seq);
+	seq = read_seqbegin(&resv->seq);
 	rcu_read_lock();
 
 	fobj = rcu_dereference(resv->fence);
@@ -177,7 +177,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 	else
 		shared_count = 0;
 	fence_excl = rcu_dereference(resv->fence_excl);
-	if (read_seqcount_retry(&resv->seq, seq)) {
+	if (read_seqretry(&resv->seq, seq)) {
 		rcu_read_unlock();
 		goto retry;
 	}
@@ -1034,12 +1034,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
 
 		robj = buf_obj->resv;
 		while (true) {
-			seq = read_seqcount_begin(&robj->seq);
+			seq = read_seqbegin(&robj->seq);
 			rcu_read_lock();
 			fobj = rcu_dereference(robj->fence);
 			shared_count = fobj ? fobj->shared_count : 0;
 			fence = rcu_dereference(robj->fence_excl);
-			if (!read_seqcount_retry(&robj->seq, seq))
+			if (!read_seqretry(&robj->seq, seq))
 				break;
 			rcu_read_unlock();
 		}
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 4d32e2c678626..37d8f6b18ef90 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -110,15 +110,13 @@ int reservation_object_reserve_shared(struct reservation_object *obj,
 	new->shared_count = j;
 	new->shared_max = max;
 
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
+	write_seqlock(&obj->seq);
 	/*
 	 * RCU_INIT_POINTER can be used here,
 	 * seqcount provides the necessary barriers
 	 */
 	RCU_INIT_POINTER(obj->fence, new);
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
+	write_sequnlock(&obj->seq);
 
 	if (!old)
 		return 0;
@@ -158,8 +156,7 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
 	fobj = reservation_object_get_list(obj);
 	count = fobj->shared_count;
 
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
+	write_seqlock(&obj->seq);
 
 	for (i = 0; i < count; ++i) {
 		struct dma_fence *old_fence;
@@ -181,8 +178,7 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
 	/* pointer update must be visible before we extend the shared_count */
 	smp_store_mb(fobj->shared_count, count);
 
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
+	write_sequnlock(&obj->seq);
 }
 EXPORT_SYMBOL(reservation_object_add_shared_fence);
 
@@ -209,14 +205,11 @@ void reservation_object_add_excl_fence(struct reservation_object *obj,
 	if (fence)
 		dma_fence_get(fence);
 
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
-	/* write_seqcount_begin provides the necessary memory barrier */
+	write_seqlock(&obj->seq);
 	RCU_INIT_POINTER(obj->fence_excl, fence);
 	if (old)
 		old->shared_count = 0;
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
+	write_sequnlock(&obj->seq);
 
 	/* inplace update, no shared fences */
 	while (i--)
@@ -298,13 +291,10 @@ int reservation_object_copy_fences(struct reservation_object *dst,
 	src_list = reservation_object_get_list(dst);
 	old = reservation_object_get_excl(dst);
 
-	preempt_disable();
-	write_seqcount_begin(&dst->seq);
-	/* write_seqcount_begin provides the necessary memory barrier */
+	write_seqlock(&dst->seq);
 	RCU_INIT_POINTER(dst->fence_excl, new);
 	RCU_INIT_POINTER(dst->fence, dst_list);
-	write_seqcount_end(&dst->seq);
-	preempt_enable();
+	write_sequnlock(&dst->seq);
 
 	if (src_list)
 		kfree_rcu(src_list, rcu);
@@ -345,7 +335,7 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
 		shared_count = i = 0;
 
 		rcu_read_lock();
-		seq = read_seqcount_begin(&obj->seq);
+		seq = read_seqbegin(&obj->seq);
 
 		fence_excl = rcu_dereference(obj->fence_excl);
 		if (fence_excl && !dma_fence_get_rcu(fence_excl))
@@ -390,7 +380,7 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
 			}
 		}
 
-		if (i != shared_count || read_seqcount_retry(&obj->seq, seq)) {
+		if (i != shared_count || read_seqretry(&obj->seq, seq)) {
 			while (i--)
 				dma_fence_put(shared[i]);
 			dma_fence_put(fence_excl);
@@ -439,7 +429,7 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
 
 retry:
 	shared_count = 0;
-	seq = read_seqcount_begin(&obj->seq);
+	seq = read_seqbegin(&obj->seq);
 	rcu_read_lock();
 	i = -1;
 
@@ -486,7 +476,7 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
 
 	rcu_read_unlock();
 	if (fence) {
-		if (read_seqcount_retry(&obj->seq, seq)) {
+		if (read_seqretry(&obj->seq, seq)) {
 			dma_fence_put(fence);
 			goto retry;
 		}
@@ -542,7 +532,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
 retry:
 	ret = true;
 	shared_count = 0;
-	seq = read_seqcount_begin(&obj->seq);
+	seq = read_seqbegin(&obj->seq);
 
 	if (test_all) {
 		unsigned i;
@@ -563,7 +553,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
 				break;
 		}
 
-		if (read_seqcount_retry(&obj->seq, seq))
+		if (read_seqretry(&obj->seq, seq))
 			goto retry;
 	}
 
@@ -576,7 +566,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
 			if (ret < 0)
 				goto retry;
 
-			if (read_seqcount_retry(&obj->seq, seq))
+			if (read_seqretry(&obj->seq, seq))
 				goto retry;
 		}
 	}
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index a6e5184d436c9..b5fbd16034122 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -250,11 +250,9 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
 	new->shared_count = k;
 
 	/* Install the new fence list, seqcount provides the barriers */
-	preempt_disable();
-	write_seqcount_begin(&resv->seq);
+	write_seqlock(&resv->seq);
 	RCU_INIT_POINTER(resv->fence, new);
-	write_seqcount_end(&resv->seq);
-	preempt_enable();
+	write_sequnlock(&resv->seq);
 
 	/* Drop the references to the removed fences or move them to ef_list */
 	for (i = j, k = 0; i < old->shared_count; ++i) {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ad01c92aaf748..2910a133077a3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -449,7 +449,7 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 				 unsigned int flags,
 				 long timeout)
 {
-	unsigned int seq = __read_seqcount_begin(&resv->seq);
+	unsigned int seq = read_seqbegin(&resv->seq);
 	struct dma_fence *excl;
 	bool prune_fences = false;
 
@@ -500,9 +500,9 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 	 * signaled and that the reservation object has not been changed (i.e.
 	 * no new fences have been added).
 	 */
-	if (prune_fences && !__read_seqcount_retry(&resv->seq, seq)) {
+	if (prune_fences && !read_seqretry(&resv->seq, seq)) {
 		if (reservation_object_trylock(resv)) {
-			if (!__read_seqcount_retry(&resv->seq, seq))
+			if (!read_seqretry(&resv->seq, seq))
 				reservation_object_add_excl_fence(resv, NULL);
 			reservation_object_unlock(resv);
 		}
@@ -3943,7 +3943,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 	 *
 	 */
 retry:
-	seq = raw_read_seqcount(&obj->resv->seq);
+	seq = read_seqbegin(&obj->resv->seq);
 
 	/* Translate the exclusive fence to the READ *and* WRITE engine */
 	args->busy = busy_check_writer(rcu_dereference(obj->resv->fence_excl));
@@ -3961,7 +3961,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 		}
 	}
 
-	if (args->busy && read_seqcount_retry(&obj->resv->seq, seq))
+	if (args->busy && read_seqretry(&obj->resv->seq, seq))
 		goto retry;
 
 	err = 0;
diff --git a/include/linux/reservation.h b/include/linux/reservation.h
index ee750765cc941..11cc05f489365 100644
--- a/include/linux/reservation.h
+++ b/include/linux/reservation.h
@@ -71,7 +71,7 @@ struct reservation_object_list {
  */
 struct reservation_object {
 	struct ww_mutex lock;
-	seqcount_t seq;
+	seqlock_t seq;
 
 	struct dma_fence __rcu *fence_excl;
 	struct reservation_object_list __rcu *fence;
@@ -90,7 +90,7 @@ reservation_object_init(struct reservation_object *obj)
 {
 	ww_mutex_init(&obj->lock, &reservation_ww_class);
 
-	__seqcount_init(&obj->seq, reservation_seqcount_string, &reservation_seqcount_class);
+	seqlock_init(&obj->seq);
 	RCU_INIT_POINTER(obj->fence, NULL);
 	RCU_INIT_POINTER(obj->fence_excl, NULL);
 }
-- 
2.23.0.rc1


> Best regards,
> 
> 
> YC

Sebastian