Re: [RFC PATCH 6.12.y 4/5] mm/damon/core: filter out damos address filter-split failed region

[sashiko-bot@kernel.org]

> When an address type DAMOS filter is configured, DAMOS tries to split the
> region for the filter range, and apply DAMOS action to the filter-in
> region.  The split operation (damon_split_region_at()) could fail from
> allocation failure under extreme memory pressure.  In the case, DAMOS
> action could be applied more or less than expected, ignoring the address
> filter.
> 
> The issue only rarely happens under extreme memory pressure.  No crash or
> leak happens.  Occasionally not applying the action to a few regions
> shouldn't be a real problem.  But applying the action to a region that the
> user has excluded via address filter could be a surprise depending on the
> use case.  It is only theoretical.  No such real case is found yet.
> 
> Filter out the entire region if the split is failed.  Update
> damos_filter_match() signature to receive the error from split.  Also
> update kunit tests for the updated signature.
> 
> The issue was discovered [1] by sashiko.
> 
> Link: https://lore.kernel.org/20261020004119.106690-1-sj@kernel.org
> Link: https://lore.kernel.org/20260801203121.117449-1-sj@kernel.org [1]
> Fixes: ab9bda001b68 ("mm/damon/core: introduce address range type damos filter")
> Signed-off-by: SJ Park <sj@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Cc: <stable@vger.kernel.org> # 6.6.x
> (cherry picked from commit bbeec2d8324d7aac438bb12dd2d22b184e0a8d43)
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues.

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