Re: [PATCH v3 1/2] mm/damon/lru_sort: validate min_region_size to be power of 2

[SeongJae Park <sj@kernel.org>]

On Mon,  6 Apr 2026 17:41:16 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> On Sat,  4 Apr 2026 13:30:43 -0700 SeongJae Park <sj@kernel.org> wrote:
> 
> > On Sat,  4 Apr 2026 17:11:22 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:
> > 
> > > [...]
> > > I think this deserves Cc stable@ because:
> > > - The issue can be triggered by accidental user misconfiguration
> > > - It causes kdamond termination and hard to recover/restart. Once
> > >   triggered, kdamond remains in an unusable state, and I have not found
> > >   a way to recover/restart it through the sysfs interface without a
> > >   system reboot.
> > > - The fix is small and low-risk
> > > - It improves user experience on stable kernels
> > 
> > Thank you for elaborating this.  I now think this deserves Cc-ing stable@.
> 
> Thank you for agreeing to Cc stable@.
> 
> > Let's make sure the user impact is clearly documented on the commit message.
> > Also, the code change itself and the current commit message is not clearly
> > explaining how the real problem (DAMON cannot be restarted) can happen.  Please
> > add the description in the next revision.
> 
> I will add an explanation of why DAMON cannot be restarted in the next
> revision.
> 
> > [...]
> > 
> > > 
> > > > For stable@ Cc-ing patches, more clearly describing the user impact would be
> > > > nice, and helpful for judging if it deserves that.  Could you please elaborate?
> > > 
> > > I will add a "User Impact" section in v4's commit message:
> > 
> > Yes, please add this kind of message that make clear what is the user impact.
> > 
> > > 
> > >     User Impact
> > >     ===========
> > >     Currently, if a user commit an invalid 'addr_unit', kdamond may
> > >     terminate abruptly. Once terminated, it cannot be easily restarted
> > >     via sysfs, pontentially requiring a system reboot to restore DAMON
> > >     functionality. This patch prevent such termination by validating
> > >     parameters (addr_unit and min_region_sz) early.
> > 
> > You mentioned it cannot be restarted above.  The above message sounds like
> > there is a way to restart it via sysfs, though it is not easy.  Please make it
> > clear and consistent.  As I also requested above, please add the internal
> > mechanism of how that makes restart unable.  This itself doesn't explain it.
> 
> Thank you for your correction. I will make the description clear and
> consistent, and also explain the internal mechanism 
> (the 'maybe_corrupted' flag and why writing to 'enabled' cannot recover
> it).

Sounds all good :)

> 
> Note: 
> Please excuse my slower responses in the coming weeks, as I have
> upcoming exams. I will be most active and able to follow up during
> weekend (Friday/Saturday).

No worries, take your time :)


Thanks,
SJ

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