Re: [PATCH] mm/damon: validate addr_unit to be power of 2

[SeongJae Park <sj@kernel.org>]

On Sat, 28 Mar 2026 06:29:37 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Sat, 28 Mar 2026 10:26:51 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:
> 
> [...]
> > Just to make sure I captured the full context, in my earlier follow-ups
> > [1][2] (in case they got folded in your email client):
> > 
> > - Does the current kdamond termination on invalid user input align with
> >   your design goal mentioned in [3] (stopping only for "internal
> >   errors")?
> 
> No.  I still think it would be better to avoid wrong input-caused termination.
> But in a simple way.  Also, it would be better to be consistent.
> 
> > 
> > - Would a lightweight fix be acceptable? For example, performing
> >   validation at the very beginning of damon_commit_ctx(), and returning
> >   -EINVAL before setting 'maybe_corrupted' to true. Since no
> >   modifications to 'dst' would have occurred, kdamond could safely
> >   continue with its old configuration.
> 
> I suggested you to try something similar to what DAMON_SYSFS is doing.  But I
> didn't get your response to the idea yet.  Could you please let me know what do
> you think about the approach?

I was thinking this one more time.  So you want to ensure DAMON_RECLAIM and
DAMON_LRU_SORT not passing wrong addr_unit to damon_commit_ctx(), right?  And
that's required because exisitng inputs validations of DAMON_RECLAIM and
DAMON_LRU_SORT are not checking that.  Why don't you add the just one more
check there?

I remember I was saying this kind of change would be a kind of whack-a-mole and
therefore prefer DAMON_SYSFS type damon_commit_ctx() based checking.  But
that's not a small change.  Just adding yet another simple check on existing
validation logic should be fine and small.


Thanks,
SJ

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