Re: [RFC PATCH] mm/damon/core: remove unreachable damos charge_{target,addr}_from

[sashiko-bot@kernel.org]

> damos_quota->charge_{target,addr}_from saves the target and region the
> scheme's quota limit is reached.  damos_skip_charged_region() skips the
> target and regions before the point.  The target that was assigned to
> charge_target_from could be dynamically removed from the context by the
> runtime parameters update (aka commit) feature.  In this case,
> damos_skip_charged_region() cannot find if the point is passed or not,
> so the scheme is effectively disabled.
> 
> Similarly, the user could also remove all the regions of the target
> using the runtime parameters update feature.  It would be uncommon to do
> that, but it is a supported feature.  Because the skip pointer detection
> logic (damos_skip_charged_region()) works for each region of targets,
> this result in the logic is entirely skipped and the scheme is
> effectively disabled again.
> 
> The user impact is that the DAMOS scheme could suddenly stop working
> under certain uses of the runtime parameters update feature.  It could
> surprise users. No crash or leak happens though.  Users could also
> simply work around by re-installing the scheme.
> 
> Catch the corner cases in damos_adjust_quota() and reset the pointers.
> 
> Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update")
> Cc: <stable@vger.kernel.org> # 5.19.x
> Closes: https://sashiko.dev/#/bug/linux-cd0c55fc-0cc8-45d8-9637-3334811c49b8
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues.

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