Re: [PATCH v2] mm/shrinker: Fix refcount leak in shrink_slab_memcg()

[Qi Zheng]

On 2/4/26 11:35 AM, Altan Hacigumus wrote:
> When kmem is disabled for memcg, slab-backed shrinkers are skipped.
> However, shrink_slab_memcg() doesn't drop the reference acquired via
> shrinker_try_get() before continuing.
> 
> Add the missing shrinker_put().
> 
> Also, since memcg_kmem_online() and shrinker flags cannot change
> dynamically, remove the shrinker from the bitmap to avoid unnecessary
> future scans.
> 
> Fixes: 50d09da8e119 ("mm: shrinker: make memcg slab shrink lockless")
> Suggested-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

You identified and fixed this issue independently, not based on my
suggestion, so this tag is unnecessary. ;)

(I guess Andrew can help remove this tag)

Thanks,
Qi

> Acked-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/r/20260203073757.135088-1-ahacigu.linux@xxxxxxxxx
> Signed-off-by: Altan Hacigumus <ahacigu.linux@xxxxxxxxx>
> ---
> Changes in v2:
> - Use clear_bit() to remove shrinker from bitmap instead of just skipping
> ---
>   mm/shrinker.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index 4a93fd433689..68dc7b4242f2 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -544,8 +544,11 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
>   
>   			/* Call non-slab shrinkers even though kmem is disabled */
>   			if (!memcg_kmem_online() &&
> -			    !(shrinker->flags & SHRINKER_NONSLAB))
> +			    !(shrinker->flags & SHRINKER_NONSLAB)) {
> +				clear_bit(offset, unit->map);
> +				shrinker_put(shrinker);
>   				continue;
> +			}
>   
>   			ret = do_shrink_slab(&sc, shrinker, priority);
>   			if (ret == SHRINK_EMPTY) {