Re: [PATCH] mm/damon/sysfs: do not ignore callback's return value in damon_sysfs_damon_call()

[SeongJae Park <sj@kernel.org>]

+ Andrew

On Sat, 20 Sep 2025 05:11:31 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Sat, 20 Sep 2025 19:52:36 +0900 Akinobu Mita <akinobu.mita@gmail.com> wrote:
> 
> > The callback return value is ignored in damon_sysfs_damon_call(), which
> > means that it is not possible to detect invalid user input when writing
> > commands such as 'commit' to /sys/kernel/mm/damon/admin/kdamonds/<K>/state.
> > Fix it.
> 
> Thank you for finding this issue, Akinobu!  Before the introduction of
> damon_sysfs_damon_call() and its usages, DAMON sysfs interface was returning an
> error in case of such command failures.  So this is fixing a user-visible
> unintended behavior change.  Hence this may deserve Cc-ing stable@ in my
> opinion.
> 
> > 
> 
> So, below may better to be added?
> 
> Fixes: f64539dcdb87 ("mm/damon/sysfs: use damon_call() for update_schemes_stats")
> Cc: <stable@vger.ekrnel.org> # v6.14.x
> 
> > Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> 
> Reviewed-by: SeongJae Park <sj@kernel.org>
> 
> > ---
> >  mm/damon/sysfs.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> > index fe4e73d0ebbb..97e16f00f23e 100644
> > --- a/mm/damon/sysfs.c
> > +++ b/mm/damon/sysfs.c
> > @@ -1627,12 +1627,15 @@ static int damon_sysfs_damon_call(int (*fn)(void *data),
> >  		struct damon_sysfs_kdamond *kdamond)
> >  {
> >  	struct damon_call_control call_control = {};
> > +	int err;
> >  
> >  	if (!kdamond->damon_ctx)
> >  		return -EINVAL;
> >  	call_control.fn = fn;
> >  	call_control.data = kdamond;
> > -	return damon_call(kdamond->damon_ctx, &call_control);
> > +	err = damon_call(kdamond->damon_ctx, &call_control);
> > +
> 
> I think the above new line is not really needed, but it is definitely trivial.
> 
> > +	return err ? err : call_control.return_code;
> >  }
> >  
> >  struct damon_sysfs_schemes_walk_data {
> > -- 
> > 2.43.0
> 
> 
> Thanks,
> SJ
>