Re: [PATCH v2] zram: fix idle age_sec underflow in idle_store()

[Hao Jia <jiahao.kernel@gmail.com>]

On 2026/8/31 17:38, Sergey Senozhatsky wrote:
> On (26/08/31 16:37), Hao Jia wrote:
>> On 2026/8/31 12:15, Sergey Senozhatsky wrote:
>>> On (26/08/28 10:24), Andrew Morton wrote:
>>>> On Fri, 28 Aug 2026 16:31:49 +0800 Hao Jia <jiahao.kernel@gmail.com> wrote:
>>> [..]
>>>>
>>>> Thanks.  Sashiko asked a couple of questions about this change:
>>>> 	https://sashiko.dev/#/patchset/20260828083149.45760-1-jiahao.kernel@gmail.com
>>>
>>>
>>>> Does this early return prevent marking valid boot-time pages as idle?
>>>> When a page is accessed during the first second of system boot, its ac_time
>>>> would be 0.
>>>
>>> There is no possibility for zram to hold pages during first second of
>>> system boot, regardless of whether zram was configured as a swap device
>>> or as a block device (mount-ed with real filesystem).
>>>
>>>
>>>> Can the early return above bypass this zram device initialization check?
>>>
>>> We already do that, e.g. when kstrtouint(buf, 0, &age_sec) fails.  Apart
>>> from that, that's not how one checks if device was initialized.  We may
>>> want to consolidate those checks, just for symmetry.
>>
>> Agreed on both points -- the early return is not a new "bypass", and
>> the write() return value was never a way to probe init state.
>>
>> How about moving the init_done() check to the top, so all the early
>> returns sit behind the same device-state check?
> 
> Yeah, I don't know...  Moving it under device lock doesn't buy us
> anything.  We don't need device lock to validate integer rangers,
> etc.  There are validations that we need to do under device lock
> because those require a consistent device state.  But things like
> "is system uptime less than supplied sysfs data" don't logically
> require a device lock.

Thanks for the clarification. The current patch is enough, so no change 
is needed.

Thanks,
Hao