FAILED: patch "[PATCH] drm/amdgpu: workaround for TLB seq race" failed to apply to 6.0-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.0-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Possible dependencies:

f9e694964503 ("drm/amdgpu: workaround for TLB seq race")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f9e69496450352fa0504fd5a8fd9134b31116558 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>
Date: Wed, 2 Nov 2022 14:55:13 +0100
Subject: [PATCH] drm/amdgpu: workaround for TLB seq race
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

It can happen that we query the sequence value before the callback
had a chance to run.

Workaround that by grabbing the fence lock and releasing it again.
Should be replaced by hw handling soon.

Signed-off-by: Christian König <christian.koenig@amd.com>
CC: stable@vger.kernel.org # 5.19+
Fixes: 5255e146c99a6 ("drm/amdgpu: rework TLB flushing")
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2113
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Philip Yang <Philip.Yang@amd.com>
Tested-by: Stefan Springer <stefanspr94@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index 83acb7bd80fe..1d31771b4230 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -492,6 +492,21 @@ void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct seq_file *m);
  */
 static inline uint64_t amdgpu_vm_tlb_seq(struct amdgpu_vm *vm)
 {
+	unsigned long flags;
+	spinlock_t *lock;
+
+	/*
+	 * Workaround to stop racing between the fence signaling and handling
+	 * the cb. The lock is static after initially setting it up, just make
+	 * sure that the dma_fence structure isn't freed up.
+	 */
+	rcu_read_lock();
+	lock = vm->last_tlb_flush->lock;
+	rcu_read_unlock();
+
+	spin_lock_irqsave(lock, flags);
+	spin_unlock_irqrestore(lock, flags);
+
 	return atomic64_read(&vm->tlb_seq);
 }