Re: [PATCH 6/8] mm/vmalloc: Defer freeing partly initialized vm_struct

[Michal Hocko <mhocko@suse.com>]

On Thu 07-08-25 09:58:08, Uladzislau Rezki wrote:
> __vmalloc_area_node() may call free_vmap_area() or vfree() on
> error paths, both of which can sleep. This becomes problematic
> if the function is invoked from an atomic context, such as when
> GFP_ATOMIC or GFP_NOWAIT is passed via gfp_mask.
> 
> To fix this, unify error paths and defer the cleanup of partly
> initialized vm_struct objects to a workqueue. This ensures that
> freeing happens in a process context and avoids invalid sleeps
> in atomic regions.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

LGTM
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!

> ---
>  include/linux/vmalloc.h |  6 +++++-
>  mm/vmalloc.c            | 34 +++++++++++++++++++++++++++++++---
>  2 files changed, 36 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index fdc9aeb74a44..b1425fae8cbf 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -50,7 +50,11 @@ struct iov_iter;		/* in uio.h */
>  #endif
>  
>  struct vm_struct {
> -	struct vm_struct	*next;
> +	union {
> +		struct vm_struct *next;	  /* Early registration of vm_areas. */
> +		struct llist_node llnode; /* Asynchronous freeing on error paths. */
> +	};
> +
>  	void			*addr;
>  	unsigned long		size;
>  	unsigned long		flags;
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 7f48a54ec108..2424f80d524a 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3680,6 +3680,35 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  	return nr_allocated;
>  }
>  
> +static LLIST_HEAD(pending_vm_area_cleanup);
> +static void cleanup_vm_area_work(struct work_struct *work)
> +{
> +	struct vm_struct *area, *tmp;
> +	struct llist_node *head;
> +
> +	head = llist_del_all(&pending_vm_area_cleanup);
> +	if (!head)
> +		return;
> +
> +	llist_for_each_entry_safe(area, tmp, head, llnode) {
> +		if (!area->pages)
> +			free_vm_area(area);
> +		else
> +			vfree(area->addr);
> +	}
> +}
> +
> +/*
> + * Helper for __vmalloc_area_node() to defer cleanup
> + * of partially initialized vm_struct in error paths.
> + */
> +static DECLARE_WORK(cleanup_vm_area, cleanup_vm_area_work);
> +static void defer_vm_area_cleanup(struct vm_struct *area)
> +{
> +	if (llist_add(&area->llnode, &pending_vm_area_cleanup))
> +		schedule_work(&cleanup_vm_area);
> +}
> +
>  static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  				 pgprot_t prot, unsigned int page_shift,
>  				 int node)
> @@ -3711,8 +3740,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  		warn_alloc(gfp_mask, NULL,
>  			"vmalloc error: size %lu, failed to allocated page array size %lu",
>  			nr_small_pages * PAGE_SIZE, array_size);
> -		free_vm_area(area);
> -		return NULL;
> +		goto fail;
>  	}
>  
>  	set_vm_area_page_order(area, page_shift - PAGE_SHIFT);
> @@ -3789,7 +3817,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  	return area->addr;
>  
>  fail:
> -	vfree(area->addr);
> +	defer_vm_area_cleanup(area);
>  	return NULL;
>  }
>  
> -- 
> 2.39.5

-- 
Michal Hocko
SUSE Labs