Re: [PATCH v3 2/3] mm: memcontrol: change val type to long in __mod_memcg_{lruvec_}state()

[Zi Yan <ziy@nvidia.com>]

On 27 Mar 2026, at 6:16, Qi Zheng wrote:

> From: Qi Zheng <zhengqi.arch@bytedance.com>
>
> The __mod_memcg_state() and __mod_memcg_lruvec_state() functions are also
> used to reparent non-hierarchical stats. In this scenario, the values
> passed to them are accumulated statistics that might be extremely large
> and exceed the upper limit of a 32-bit integer.
>
> Change the val parameter type from int to long in these functions and
> their corresponding tracepoints (memcg_rstat_stats) to prevent potential
> overflow issues.
>
> After that, in memcg_state_val_in_pages(), if the passed val is negative,
> the expression val * unit / PAGE_SIZE could be implicitly converted to a
> massive positive number when compared with 1UL in the max() macro.
> This leads to returning an incorrect massive positive value.
>
> Fix this by using abs(val) to calculate the magnitude first, and then
> restoring the sign of the value before returning the result. Additionally,
> use mult_frac() to prevent potential overflow during the multiplication of
> val and unit.
>
> Reported-by: Harry Yoo (Oracle) <harry@kernel.org>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> ---
>  include/trace/events/memcg.h | 10 +++++-----
>  mm/memcontrol.c              | 18 ++++++++++++------
>  2 files changed, 17 insertions(+), 11 deletions(-)
>
Acked-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi