Re: [PATCH v6 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create_bank()` fails

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

On 4/4/22 12:43 AM, Ammar Faizi wrote:
> On 4/4/22 12:03 AM, Thomas Gleixner wrote:
>> On Tue, Mar 29 2022 at 17:47, Ammar Faizi wrote:
>>
>>> In mce_threshold_create_device(), if threshold_create_bank() fails, the
>>> @bp will be leaked, because the call to mce_threshold_remove_device()
>>> will not free the @bp. mce_threshold_remove_device() frees
>>> @threshold_banks. At that point, the @bp has not been written to
>>> @threshold_banks, @threshold_banks is NULL, so the call is just a nop.
>>>
>>> Fix this by extracting the cleanup part into a new static function
>>> __threshold_remove_device(), then call it from create/remove device
>>> functions.
>>
>> The way simpler fix is to move
>>
>>>       }
>>>       this_cpu_write(threshold_banks, bp);
>>
>> before the loop. That's safe because the banks cannot yet be reached via
>> an MCE as the vector is not yet enabled:
>>>       if (thresholding_irq_en)
>>>           mce_threshold_vector = amd_threshold_interrupt;
> Thomas,
> 
> I did like what you said (in the patch v4), but after Yazen and Borislav
> reviewed it, we got a conclusion that it's not safe.
> 
> See [1] and [2] for the full message.
> 
> [1]: https://lore.kernel.org/lkml/YkFsQhpGGXIFTMyp@zn.tnic/
> [2]: https://lore.kernel.org/lkml/Yh+oyD%2F5M3TW5ZMM@yaz-ubuntu/
> 
> Yazen, Borislav, please take a deeper look on this again. I will send
> a v7 revision to really make it simpler by moving that "per-CPU var write"
> before the loop.

(only if it's really safe)

-- 
Ammar Faizi