Re: [PATCH] mm/damon/core: validate ranges in damon_set_regions()

[SJ Park <sj@kernel.org>]

On Mon, 29 Jun 2026 20:52:19 -0700 SJ Park <sj@kernel.org> wrote:

> DAMON core logic assumes zero length regions don't exist.  However, a
> few DAMON API callers including DAMON_SYSFS, DAMON_RECLAIM and
> DAMON_LRU_SORT allow users to set empty monitoring target regions.  This
> could result in WARN_ONCE() on CONFIG_DAMON_DEBUG_SANITY enabled kernel,
> and divide-by-zero from damon_merge_two_regions().
> 
> For example, the WANR_ONCE() can be triggered like below.
> 
>     # grep DAMON_DEBUG_SANITY /boot/config-$(uname -r)
>     # CONFIG_DAMON_DEBUG_SANITY=y
>     # damo start
>     # cd /sys/kernel/mm/damon/admin/kdamonds/0
>     # echo 0 > contexts/0/targets/0/regions/0/start
>     # echo 0 > contexts/0/targets/0/regions/0/end
>     # echo commit > state
>     # dmesg
>     [....]
>     [   73.705780] ------------[ cut here ]------------
>     [   73.707552] start 0 >= end 0
>     [   73.708452] WARNING: mm/damon/core.c:359 at damon_new_region+0x6e/0x80, CPU#1: kdamond.0/758
>     [...]
> 
> All DAMON API callers eventually use damon_set_regions() to setup the
> regions.  Add the validation logic in the function.

Sashiko found a pre-existing issue, and it is not a blocker of this patch in my
opinion.  Read my reply [1] to Sashiko review for more details.  So this patch
is good to go.

[1] https://lore.kernel.org/20260630041806.151124-1-sj@kernel.org


Thanks,
SJ

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