Re: [PATCH] mm/damon/core: avoid destroyed target reference from DAMOS quota

[SeongJae Park <sj@kernel.org>]

On Sat, 17 May 2025 23:18:52 +0900 Akinobu Mita <akinobu.mita@gmail.com> wrote:

> When the number of the monitoring targets in running contexts is reduced,
> there may be DAMOS quotas referencing the targets that will be destroyed.
> 
> Applying the scheme action for such DAMOS scheme will be skipped forever
> looking for the starting part of the region for the destroyed monitoring
> target.

Nice catch!

> 
> To fix this issue, when the monitoring target is destroyed, reset the
> starting part for all DAMOS quotas that reference the target.
> 

I think this deserves below Fixes: tag?

Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update")

For a clarification.  The worst scenario consequence of this issue is DAMOS
unexpectedly doing less or zero works under certain setups.  No horrible
problems such as a use after free will happen, though, since quota handling
code references quota.charge_target_from, but does not de-reference it.

So I don't think this deserves Cc-ing stable@, but I'll let stable@ maintainers
decide, as usual.

> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: SeongJae Park <sj@kernel.org>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

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