Re: [PATCH v6 1/2] drm/amdgpu: add debugfs for reset registers list

["Somalapuram, Amaranath" <asomalap@amd.com>]

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On 2/16/2022 3:41 PM, Christian König wrote:
> Am 16.02.22 um 10:49 schrieb Somalapuram Amaranath:
>> List of register populated for dump collection during the GPU reset.
>>
>> Signed-off-by: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu.h         |  5 ++
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 95 +++++++++++++++++++++
>>   2 files changed, 100 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> index b85b67a88a3d..57965316873b 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> @@ -1097,6 +1097,11 @@ struct amdgpu_device {
>>         struct amdgpu_reset_control     *reset_cntl;
>>       uint32_t ip_versions[HW_ID_MAX][HWIP_MAX_INSTANCE];
>> +
>> +    /* reset dump register */
>> +    uint32_t            *reset_dump_reg_list;
>> +    int                             n_regs;
>> +    struct mutex            reset_dump_mutex;
>
> I think we should rather use the reset lock for this instead of 
> introducing just another mutex.
>
>>   };
>>     static inline struct amdgpu_device *drm_to_adev(struct drm_device 
>> *ddev)
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> index 164d6a9e9fbb..faf985c7cb93 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> @@ -1609,6 +1609,98 @@ DEFINE_DEBUGFS_ATTRIBUTE(fops_ib_preempt, NULL,
>>   DEFINE_DEBUGFS_ATTRIBUTE(fops_sclk_set, NULL,
>>               amdgpu_debugfs_sclk_set, "%llu\n");
>>   +static ssize_t amdgpu_reset_dump_register_list_read(struct file *f,
>> +                char __user *buf, size_t size, loff_t *pos)
>> +{
>> +    struct amdgpu_device *adev = (struct amdgpu_device 
>> *)file_inode(f)->i_private;
>> +    char reg_offset[11];
>> +    int i, r, len = 0;
>> +
>> +    if (*pos)
>> +        return 0;
>> +
>> +    if (adev->n_regs == 0)
>> +        return 0;
>> +
>> +    for (i = 0; i < adev->n_regs; i++) {
>> +        sprintf(reg_offset, "0x%x ", adev->reset_dump_reg_list[i]);
>> +        r = copy_to_user(buf + len, reg_offset, strlen(reg_offset));
>> +
>> +        if (r)
>> +            return -EFAULT;
>> +
>> +        len += strlen(reg_offset);
>> +    }
>
> You need to hold the lock protecting adev->reset_dump_reg_list and 
> adev->n_regs while accessing those.
>
> (BTW: num_regs instead of n_regs would match more what we use 
> elsewhere, but is not a must have).
>
This is read function for user and returns only list of reg offsets, I 
did not understand correctly !
>> +
>> +    r = copy_to_user(buf + len, "\n", 1);
>> +
>> +    if (r)
>> +        return -EFAULT;
>> +
>> +    len++;
>> +    *pos += len;
>> +
>> +    return len;
>> +}
>> +
>> +static ssize_t amdgpu_reset_dump_register_list_write(struct file *f,
>> +            const char __user *buf, size_t size, loff_t *pos)
>> +{
>> +    struct amdgpu_device *adev = (struct amdgpu_device 
>> *)file_inode(f)->i_private;
>> +    char *reg_offset, *reg, reg_temp[11];
>> +    static int alloc_count;
>> +    int ret, i = 0, len = 0;
>> +
>> +    do {
>> +        reg_offset = reg_temp;
>> +        memset(reg_offset,  0, 11);
>> +        ret = copy_from_user(reg_offset, buf + len, min(11, 
>> ((int)size-len)));
>> +
>> +        if (ret)
>> +            goto failed;
>> +
>> +        reg = strsep(&reg_offset, " ");
>> +
>> +        if (alloc_count <= i) {
>
>> +            adev->reset_dump_reg_list =  krealloc_array(
>> +                            adev->reset_dump_reg_list, 1,
>> +                            sizeof(uint32_t), GFP_KERNEL);
>> +            alloc_count++;
>> +        }
>> +
>> +        ret = kstrtouint(reg, 16, &adev->reset_dump_reg_list[i]);
>
> This here is modifying adev->reset_dump_reg_list as well and so must 
> be protected by a lock as well.
>
> The tricky part is that we can't allocate memory while holding this 
> lock (because we need it during reset as well).
>
> One solution for this is to read the register list into a local array 
> first and when that's done swap the local array with the one in 
> adev->reset_dump_reg_list while holding the lock.
>
> Regards,
> Christian.
>
There are 2 situations:
1st time creating list n_regs will be 0 and trace event will not be 
triggered
2nd time while updating list n_regs is already set and 
adev->reset_dump_reg_list will have some offsets address (hypothetically 
speaking *during reset + update* read values from RREG32 will mix up of 
old list and new list)
its only critical when its freed and n_regs is not 0

Regards,
S.Amarnath
>> +
>> +        if (ret)
>> +            goto failed;
>> +
>> +        len += strlen(reg) + 1;
>> +        i++;
>> +
>> +    } while (len < size);
>> +
>> +    adev->n_regs = i;
>> +
>> +    return size;
>> +
>> +failed:
>> +    mutex_lock(&adev->reset_dump_mutex);
>> +    kfree(adev->reset_dump_reg_list);
>> +    adev->reset_dump_reg_list = NULL;
>> +    alloc_count = 0;
>> +    adev->n_regs = 0;
>> +    mutex_unlock(&adev->reset_dump_mutex);
>> +    return -EFAULT;
>> +}
>> +
>> +
>> +
>> +static const struct file_operations amdgpu_reset_dump_register_list = {
>> +    .owner = THIS_MODULE,
>> +    .read = amdgpu_reset_dump_register_list_read,
>> +    .write = amdgpu_reset_dump_register_list_write,
>> +    .llseek = default_llseek
>> +};
>> +
>>   int amdgpu_debugfs_init(struct amdgpu_device *adev)
>>   {
>>       struct dentry *root = adev_to_drm(adev)->primary->debugfs_root;
>> @@ -1618,6 +1710,7 @@ int amdgpu_debugfs_init(struct amdgpu_device 
>> *adev)
>>       if (!debugfs_initialized())
>>           return 0;
>>   +    mutex_init(&adev->reset_dump_mutex);
>>       ent = debugfs_create_file("amdgpu_preempt_ib", 0600, root, adev,
>>                     &fops_ib_preempt);
>>       if (IS_ERR(ent)) {
>> @@ -1672,6 +1765,8 @@ int amdgpu_debugfs_init(struct amdgpu_device 
>> *adev)
>>                   &amdgpu_debugfs_test_ib_fops);
>>       debugfs_create_file("amdgpu_vm_info", 0444, root, adev,
>>                   &amdgpu_debugfs_vm_info_fops);
>> +    debugfs_create_file("amdgpu_reset_dump_register_list", 0644, 
>> root, adev,
>> +                &amdgpu_reset_dump_register_list);
>>         adev->debugfs_vbios_blob.data = adev->bios;
>>       adev->debugfs_vbios_blob.size = adev->bios_size;
>

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