Re: [PATCH v2] memcg: Don't call schedule_work when no spinning is allowed

[Shakeel Butt <shakeel.butt@linux.dev>]

On Fri, Sep 04, 2026 at 10:31:45AM -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")
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: David Stevens <stevensd@google.com>
> ---
> v2:
>   - Added missing includes reported by Lorenzo and kernel test robot
>   - Added Acked-by
> 
>  include/linux/memcontrol.h |  2 ++
>  mm/memcontrol.c            | 13 ++++++++++++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8170bb8066a2..4a5ef0aba475 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -23,6 +23,7 @@
>  #include <linux/writeback.h>
>  #include <linux/page-flags.h>
>  #include <linux/shrinker.h>
> +#include <linux/irq_work_types.h>
>  
>  struct mem_cgroup;
>  struct obj_cgroup;
> @@ -219,6 +220,7 @@ 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..0e8b302ca9ad 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -62,6 +62,7 @@
>  #include <linux/seq_buf.h>
>  #include <linux/sched/isolation.h>
>  #include <linux/kmemleak.h>
> +#include <linux/irq_work.h>
>  #include "internal.h"
>  #include "swap_table.h"
>  #include <net/sock.h>
> @@ -2360,6 +2361,11 @@ 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 +2758,10 @@ 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 +4138,7 @@ 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 +4347,7 @@ 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);

On RT kernels, this will put rcu grace period here while we are holding the
cgroup_mutex. Easy fix would be to use IRQ_WORK_INIT_HARD instead of
init_irq_work() in mem_cgroup_alloc.

Something like:
	memcg->high_irq_work = IRQ_WORK_INIT_HARD(high_irq_work_func);