Hi Ingo,
> On 22 Mar 2024, at 10:03, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> * Anton Altaparmakov <anton@xxxxxxxxxx> wrote:
>> Hi Dave,
>>> On 14 Mar 2024, at 15:05, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>>> On 3/14/24 07:26, Anton Altaparmakov wrote:
>>>> /* image of the saved processor state */
>>>> struct saved_context {
>>>> - /*
>>>> - * On x86_32, all segment registers except gs are saved at kernel
>>>> - * entry in pt_regs.
>>>> - */
>>>> - u16 gs;
>>>> unsigned long cr0, cr2, cr3, cr4;
>>>> u64 misc_enable;
>>>> struct saved_msrs saved_msrs;
>>>> @@ -27,6 +22,11 @@ struct saved_context {
>>>> unsigned long tr;
>>>> unsigned long safety;
>>>> unsigned long return_address;
>>>> + /*
>>>> + * On x86_32, all segment registers except gs are saved at kernel
>>>> + * entry in pt_regs.
>>>> + */
>>>> + u16 gs;
>>>> bool misc_enable_saved;
>>>> } __attribute__((packed));
>>>
>>> Isn't this just kinda poking at the symptoms? This seems to be
>>> basically the exact same bug as b0b592cf08, just with a different source
>>> of unaligned structure members.
>>
>> Yes, that is exactly the same bug. That's how we figured out the solution in fact - it is totally the same problem with another struct member...
>>
>>> There's nothing to keep folks from reintroducing these kinds of issues
>>> and evidently no way to detect when they happen without lengthy reproducers.
>>
>> Correct. But short of adding asserts / documentation that pointers must be aligned or kmemleak won't work or fixing kmemleak (which I expect is not tractical as it would become a lot slower if nothing else) not sure what else can be done.
>>
>> Given I cannot see any alternative to fixing the kmemleak failures I think it is worth applying this fix.
>>
>> Unless you have better ideas how to fix this issue?
>>
>> What I can say is that we run a lot of tests with our CI and applying
>> this fix we do not see any kmemleak issues any more whilst without it we
>> see hundreds of the above - from a single, simple test run consisting of
>> 416 individual test cases on kernel 5.10 x86 with kmemleak enabled we got
>> 20 failures due to this which is quite a lot. With this fix applied we
>> get zero kmemleak related failures.
>
> I turned this tidbit into the following paragraph in the commit:
>
> Testing:
>
> We run a lot of tests with our CI, and after applying this fix we do not
> see any kmemleak issues any more whilst without it we see hundreds of
> the above report. From a single, simple test run consisting of 416 individual test
> cases on kernel 5.10 x86 with kmemleak enabled we got 20 failures due to this,
> which is quite a lot. With this fix applied we get zero kmemleak related failures.
>
> Describing the impact of a fix in a changelog is always helpful.
That's a good idea, thank you! Also, thank you for taking the patch. Always nice not to have to maintain too many custom kernel patches!
Best regards,
Anton
>
> Thanks,
>
> Ingo
--
Anton Altaparmakov <anton at tuxera.com> (replace at with @)
Lead in File System Development, Tuxera Inc., http://www.tuxera.com/
