Re: [RFC PATCH 0/2] improve vmalloc allocation

[Shuah Khan]

On 10/23/2018 01:30 PM, Joel Fernandes wrote:
> On Tue, Oct 23, 2018 at 11:13:36AM -0600, Shuah Khan wrote:
>> On 10/23/2018 11:05 AM, Michal Hocko wrote:
>>> On Tue 23-10-18 08:26:40, Matthew Wilcox wrote:
>>>> On Tue, Oct 23, 2018 at 09:02:56AM -0600, Shuah Khan wrote:
>>> [...]
>>>>> The way it can be handled is by adding a test module under lib. test_kmod,
>>>>> test_sysctl, test_user_copy etc.
>>>>
>>>> The problem is that said module can only invoke functions which are
>>>> exported using EXPORT_SYMBOL.  And there's a cost to exporting them,
>>>> which I don't think we're willing to pay, purely to get test coverage.
>>>
>>> Yes, I think we do not want to export internal functionality which might
>>> be still interesting for the testing coverage. Maybe we want something
>>> like EXPORT_SYMBOL_KSELFTEST which would allow to link within the
>>> kselftest machinery but it wouldn't allow the same for general modules
>>> and will not give any API promisses.
>>>
>>
>> I like this proposal. I think we will open up lot of test opportunities with
>> this approach.
>>
>> Maybe we can use this stress test as a pilot and see where it takes us.
> 
> I am a bit worried that such an EXPORT_SYMBOL_KSELFTEST mechanism can be abused by
> out-of-tree module writers to call internal functionality.

That is  valid concern to consider before we go forward with the proposal.

We could wrap EXPORT_SYMBOL_KSELFTEST this in an existing debug option. This could
be fine grained for each sub-system for its debug option. We do have a few of these
now

# CONFIG_STATIC_KEYS_SELFTEST is not set
# CONFIG_BT_SELFTEST is not set
# CONFIG_DRM_DEBUG_SELFTEST is not set
# CONFIG_CHASH_SELFTEST is not set
# CONFIG_DRM_I915_SELFTEST is not set
# CONFIG_CRC32_SELFTEST is not set
# CONFIG_RANDOM32_SELFTEST is not set
# CONFIG_GLOB_SELFTEST is not set
# CONFIG_STRING_SELFTEST is not set
# CONFIG_DEBUG_LOCKING_API_SELFTESTS is not set
# CONFIG_WW_MUTEX_SELFTEST is not set
# CONFIG_ATOMIC64_SELFTEST is not set
# CONFIG_X86_DECODER_SELFTEST is not set
# CONFIG_DEBUG_NMI_SELFTEST is not set

thanks,
-- Shuah