[PATCH] drm/amdgpu: fix fdinfo race with process exit

[Philip Yang]

Get process vm root BO ref in case process is exiting and root BO is
freed, to avoid NULL pointer dereference backtrace:

BUG: unable to handle kernel NULL pointer dereference at
0000000000000000
Call Trace:
amdgpu_show_fdinfo+0xfe/0x2a0 [amdgpu]
seq_show+0x12c/0x180
seq_read+0x153/0x410
vfs_read+0x91/0x140[ 3427.206183]  ksys_read+0x4f/0xb0
do_syscall_64+0x5b/0x1a0
entry_SYSCALL_64_after_hwframe+0x65/0xca

Signed-off-by: Philip Yang <philip.y...@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c
index d94c5419ec25..fba0084bbcbf 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c
@@ -59,6 +59,7 @@ void amdgpu_show_fdinfo(struct seq_file *m, struct file *f)
        uint64_t vram_mem = 0, gtt_mem = 0, cpu_mem = 0;
        struct drm_file *file = f->private_data;
        struct amdgpu_device *adev = drm_to_adev(file->minor->dev);
+       struct amdgpu_bo *root;
        int ret;
 
        ret = amdgpu_file_to_fpriv(f, &fpriv);
@@ -69,13 +70,19 @@ void amdgpu_show_fdinfo(struct seq_file *m, struct file *f)
        dev = PCI_SLOT(adev->pdev->devfn);
        fn = PCI_FUNC(adev->pdev->devfn);
 
-       ret = amdgpu_bo_reserve(fpriv->vm.root.bo, false);
+       root = amdgpu_bo_ref(fpriv->vm.root.base.bo);
+       if (!root)
+               return;
+
+       ret = amdgpu_bo_reserve(root, false);
        if (ret) {
                DRM_ERROR("Fail to reserve bo\n");
                return;
        }
        amdgpu_vm_get_memory(&fpriv->vm, &vram_mem, &gtt_mem, &cpu_mem);
-       amdgpu_bo_unreserve(fpriv->vm.root.bo);
+       amdgpu_bo_unreserve(root);
+       amdgpu_bo_unref(&root);
+
        seq_printf(m, "pdev:\t%04x:%02x:%02x.%d\npasid:\t%u\n", domain, bus,
                        dev, fn, fpriv->vm.pasid);
        seq_printf(m, "vram mem:\t%llu kB\n", vram_mem/1024UL);
-- 
2.17.1

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