Re: [PATCH 2/4] mm/damon/sysfs: check contexts->nr before clear_schemes_tried_regions

[Josh Law]

On 20 March 2026 15:51:14 GMT, SeongJae Park <sj@xxxxxxxxxx> wrote:
>On Fri, 20 Mar 2026 15:14:54 +0000 Josh Law <objecting@xxxxxxxxxxxxx> wrote:
>
>> 
>> 
>> On 20 March 2026 14:47:40 GMT, SeongJae Park <sj@xxxxxxxxxx> wrote:
>> >On Fri, 20 Mar 2026 07:06:48 +0000 Josh Law <objecting@xxxxxxxxxxxxx> wrote:
>> >
>> >> 
>> >> 
>> >> On 20 March 2026 02:13:17 GMT, SeongJae Park <sj@xxxxxxxxxx> wrote:
>> >> >On Thu, 19 Mar 2026 15:57:40 +0000 Josh Law <objecting@xxxxxxxxxxxxx> wrote:
>[...]
>> >> >Not necessarily blocker of this patch, but seems all the issues are in a same
>> >> >category.  The third patch of this series is also fixing one of the category
>> >> >bugs.  How about fixing all at once by checking kdamond->contexts->nr at the
>> >> >beginning of damon_sysfs_handle_cmd(), like below?
>> >> >
>> >> >--- a/mm/damon/sysfs.c
>> >> >+++ b/mm/damon/sysfs.c
>> >> >@@ -2404,6 +2404,9 @@ static int damon_sysfs_update_schemes_tried_regions(
>> >> > static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
>> >> >                struct damon_sysfs_kdamond *kdamond)
>> >> > {
>> >> >+       if (cmd != DAMON_SYSFS_CMD_OFF && kdamond->contexts->nr != 1)
>> >> >+               return -EINVAL;
>> >> >+
>> >> >        switch (cmd) {
>> >> >        case DAMON_SYSFS_CMD_ON:
>> >> >                return damon_sysfs_turn_damon_on(kdamond);
>> >> >
>> >> >If we pick this, Fixes: would be deserve to the oldest buggy commit that
>> >> >introduced the first bug of this category.  It is indeed quite old.
>> >> >
>> >> >Fixes: 0ac32b8affb5 ("mm/damon/sysfs: support DAMOS stats")
>> >> >Cc: <stable@xxxxxxxxxxxxxxx> # 5.18.x
>> >> >
>> >> >
>> >> >Thanks,
>> >> >SJ
>> >> 
>> >> 
>> >> 
>> >> Hello, did you give Reviewed by you? Or not..
>> >
>> >Are you meaning Reviewed-by: tag?  If so, no, not yet.  I want to get your
>> >answer to above question first.  Could you please answer?
>> >
>> >
>> >Thanks,
>> >SJ
>> >
>> >[...]
>> 
>> 
>> Well, two is in the same catagory. But seperate fixes may be best.  Because patch 3 dont call that function, so it may be screwy, i mean, if you want me to. Ill guard it. But its a bit on the hacky side
>
>I agree there could be more cleaner way.  But these fixes need to go to stable,
>so I'd prefer a change that also easier to backport.
>
>So, yes, I want to.  Thank you for kindly accepting my suggestion.
>
>Could you please re-post this series for the first and the fourth patches as
>they are, after adding my Reviewed-by:, Fixes: and Cc: stable tags, and a patch
>checking kdamond->contexts->nr at the beginning of damon_sysfs_handle_cmd() as
>I suggested?
>
>
>Thanks,
>SJ
>
>[...]


Absolutely!

Will do