Re: [PATCH] memcg: Don't call schedule_work when no spinning is allowed

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Mon, Aug 31, 2026 at 04:43:39PM -0700, David Stevens wrote:
> Memcg charging can be done from any context, but calling schedule_work()
> isn't safe from an NMI. If memory.high is breached from a context where
> spinning isn't allowed, use irq_work to schedule the reclaim work.
>
> Fixes: 3ac4638a734a ("memcg: make memcg_rstat_updated nmi safe")
> Signed-off-by: David Stevens <stevensd@google.com>

This is in mm-unstable and breaks the build for me :)

In general - please don't rely on implicit header includes, if you're using
functions from a header that's not included, add the include because your local
config might happen to import it but another one might be broken.

$ make -j $(nproc) LLVM=1 mm/memcontrol.o
  DESCEND objtool
  CC      arch/x86/kernel/asm-offsets.s
  UPD     include/generated/asm-offsets.h
  CC      kernel/sched/rq-offsets.s
  UPD     include/generated/rq-offsets.h
  CALL    scripts/checksyscalls.sh
  CC      mm/memcontrol.o
mm/memcontrol.c:2859:6: error: call to undeclared function 'irq_work_queue'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
 2859 |                                         irq_work_queue(&memcg->high_irq_work);
      |                                         ^
mm/memcontrol.c:4234:2: error: call to undeclared function 'init_irq_work'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
 4234 |         init_irq_work(&memcg->high_irq_work, high_irq_work_func);
      |         ^
mm/memcontrol.c:4443:2: error: call to undeclared function 'irq_work_sync'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
 4443 |         irq_work_sync(&memcg->high_irq_work);
      |         ^
3 errors generated.
make[3]: *** [scripts/Makefile.build:290: mm/memcontrol.o] Error 1
make[2]: *** [scripts/Makefile.build:551: mm] Error 2
make[1]: *** [/home/lorenzo/kerndev/kernels/mm/Makefile:2229: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2

> ---
>  include/linux/memcontrol.h |  1 +
>  mm/memcontrol.c            | 12 +++++++++++-
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8170bb8066a2..036d973ceca6 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -219,6 +219,7 @@ struct mem_cgroup {
>  	spinlock_t	 peaks_lock;
>
>  	/* Range enforcement for interrupt charges */
> +	struct irq_work high_irq_work;
>  	struct work_struct high_work;
>
>  #ifdef CONFIG_ZSWAP
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6dc4888a90f3..5e2f749067cb 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c

You need to add:

#include <linux/irq_work.h> in this file.

> @@ -2360,6 +2360,11 @@ static void high_work_func(struct work_struct *work)
>  	reclaim_high(memcg, MEMCG_CHARGE_BATCH, GFP_KERNEL);
>  }
>
> +static void high_irq_work_func(struct irq_work *work)
> +{
> +	schedule_work(&container_of(work, struct mem_cgroup, high_irq_work)->high_work);
> +}
> +
>  /*
>   * Clamp the maximum sleep time per allocation batch to 2 seconds. This is
>   * enough to still cause a significant slowdown in most cases, while still
> @@ -2752,7 +2757,10 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  		/* Don't bother a random interrupted task */
>  		if (!in_task()) {
>  			if (mem_high) {
> -				schedule_work(&memcg->high_work);
> +				if (allow_spinning)
> +					schedule_work(&memcg->high_work);
> +				else
> +					irq_work_queue(&memcg->high_irq_work);
>  				break;
>  			}
>  			continue;
> @@ -4129,6 +4137,7 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
>  		goto fail;
>
>  	INIT_WORK(&memcg->high_work, high_work_func);
> +	init_irq_work(&memcg->high_irq_work, high_irq_work_func);
>  	vmpressure_init(&memcg->vmpressure);
>  	INIT_LIST_HEAD(&memcg->memory_peaks);
>  	INIT_LIST_HEAD(&memcg->swap_peaks);
> @@ -4337,6 +4346,7 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
>  		static_branch_dec(&memcg_bpf_enabled_key);
>
>  	vmpressure_cleanup(&memcg->vmpressure);
> +	irq_work_sync(&memcg->high_irq_work);
>  	cancel_work_sync(&memcg->high_work);
>  	memcg1_remove_from_trees(memcg);
>  	free_shrinker_info(memcg);
>
> base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> --
> 2.55.0.897.gb25b4bd76c-goog
>
>

--
Cheers, Lorenzo