Re: [RFC PATCH 1/3] mm/damon/core: error damos_commit_quota_goal() for zero target_value

[sashiko-bot@kernel.org]

> If a DAMOS scheme has a damos_quota_goal of zero target_value,
> damos_quota_goal() could trigger division-by-zero error.  Hence each
> DAMON API callers should do the zero target_value validation.  It is
> easy to make mistakes.  Actually such bugs in DAMON_LRU_SORT and
> DAMON_SAMPLE_MTIER were found and fixed [1].
> 
> It is better to handle the corner case only once in the core layer,
> instead of multiple places in all DAMON API callers.  One
> straightforward option is using an alternative denominator for the
> corner case in the damos_quota_goal().  However, the zero target_value
> is meaningless.  In this case, the quota goal is always evaluated as
> achieved or over-achieved.  The quota will only keep being reduced.
> 
> Simply avoid using zero target_value by adding a check in the core layer
> DAMOS quota goal parameters validation/commit path,
> damos_commit_quota_goal().  Update it to return an error in the case.
> Also update its caller to propagate the error.
> 
> [1] https://lore.kernel.org/20260803134034.15217-1-sj@kernel.org
> 
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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