get_cg_pool_unlocked() handles allocation failures under dmemcg_lock by
dropping the lock, preallocating a pool with GFP_KERNEL, and retrying the
locked lookup and creation path.

If the fallback allocation fails too, pool remains NULL. Since the loop
condition is while (!pool), the function can keep retrying instead of
propagating the allocation failure to the caller.

Set pool to ERR_PTR(-ENOMEM) when the fallback allocation fails so the
loop exits through the existing common return path. The callers already
handle ERR_PTR() from get_cg_pool_unlocked(), so this restores the
expected error path.

Fixes: b168ed458dde ("kernel/cgroup: Add "dmem" memory accounting cgroup")
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 kernel/cgroup/dmem.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 1ab1fb47f271..4753a67d0f0f 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -602,6 +602,7 @@ get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region *region)
 				pool = NULL;
 				continue;
 			}
+			pool = ERR_PTR(-ENOMEM);
 		}
 	}
 
-- 
2.43.0

On Mon, May 11, 2026 at 09:31:50AM +0800, Guopeng Zhang <zhangguopeng@kylinos.cn> wrote:
> get_cg_pool_unlocked() handles allocation failures under dmemcg_lock by
> dropping the lock, preallocating a pool with GFP_KERNEL, and retrying the
> locked lookup and creation path.
> 
> If the fallback allocation fails too, pool remains NULL. Since the loop
> condition is while (!pool), the function can keep retrying instead of
> propagating the allocation failure to the caller.

This implies that it's OK when the function keeps retrying with
allocpool != NULL (and repeated WARN_ON()s)?

> Set pool to ERR_PTR(-ENOMEM) when the fallback allocation fails so the
> loop exits through the existing common return path. The callers already
> handle ERR_PTR() from get_cg_pool_unlocked(), so this restores the
> expected error path.

If the callers can handle it, maybe there's no need to retry at all.
Perhpas dmem fellows can step in here.

> 
> Fixes: b168ed458dde ("kernel/cgroup: Add "dmem" memory accounting cgroup")
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>  kernel/cgroup/dmem.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
> index 1ab1fb47f271..4753a67d0f0f 100644
> --- a/kernel/cgroup/dmem.c
> +++ b/kernel/cgroup/dmem.c
> @@ -602,6 +602,7 @@ get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region *region)
>  				pool = NULL;

This 2nd pool zeroing seems pointless.

>  				continue;
>  			}
> +			pool = ERR_PTR(-ENOMEM);
>  		}
>  	}


HTH,
Michal