Re: [RFC v4] mm/damon: add synchronous commit for commit_inputs

[Liew Rui Yan <aethernet65535@gmail.com>]

Hi SeongJae,

Follow-up on my previous email regarding the locking concerns.

> I admit I don't have an elegant solution yet. Here are my current
> thought:
> 
> Add a timeout to wait_for_completion() (e.g.,
> wait_for_completion_timeout()), using 'damos_watermarks.interval' as the
> upper bound. This prevents indefinite blocking of 'param_lock', though
> it still holds the global lock for up to several seconds.

After further analysis, I realized that since both 'commit_inputs' and
'enabled' module parameters are protected by the global 'param_lock',
stopping kdamond gracefully (via enabled=N) is serialized with
'commit_inputs' writes. Therefore, a classic deadlock scenario should
not occur in normal operation.

However, I'm considering edge cases where kdamond might terminate
unexpectedly. In such cases, commit_inputs_store() could hold
'param_lock' indefinitely, blocking other module parameter updates
system-wide.

To mitigate this risk defensively, would you accept adding a timeout to
wait_for_completion()? This ensures 'param_lock' is eventually released
even if kdamond fails unexpectedly.

Please let me know your preference. :>

Best regards,
Rui Yan