[PATCH v6 1/2] drm/amdgpu: add debugfs for reset registers list
Somalapuram, Amaranath
asomalap at amd.com
Thu Feb 17 07:54:58 UTC 2022
On 2/16/2022 8:26 PM, Christian König wrote:
> Am 16.02.22 um 14:11 schrieb Somalapuram, Amaranath:
>>
>> 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 at 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(®_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.
>>>
krealloc_array should be inside lock or outside lock? this may be problem.
Regards,
S.Amarnath
>>> 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
>
> No, that won't work like this. See you *must* always hold a lock when
> reading or writing the array.
>
> Otherwise it is perfectly possible that one thread sees only halve of
> the updates of another thread.
>
> The only alternative would be RCU, atomic replace and manual barrier
> handling, but that would be complete overkill for that feature.
>
> Regards,
> Christian.
>
>>
>> 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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