linux-kernel - Re: [PATCH 3/8] mm/vmalloc: Support non-blocking GFP flags in alloc_vmap

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Message-ID: <aJSMFgvrLEN-nwdT@tiehlicka>
Date: Thu, 7 Aug 2025 13:20:54 +0200
From: Michal Hocko <mhocko@...e.com>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Baoquan He <bhe@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/8] mm/vmalloc: Support non-blocking GFP flags in
 alloc_vmap_area()

On Thu 07-08-25 09:58:05, Uladzislau Rezki wrote:
> alloc_vmap_area() currently assumes that sleeping is allowed during
> allocation. This is not true for callers which pass non-blocking
> GFP flags, such as GFP_ATOMIC or GFP_NOWAIT.

Those are currently not allowed so it would be better to mention this is
a preparation for those to _be_ supported later in the series.
 
> This patch adds logic to detect whether the given gfp_mask permits
> blocking. It avoids invoking might_sleep() or falling back to reclaim
> path if blocking is not allowed.
> 
> This makes alloc_vmap_area() safer for use in non-sleeping contexts,
> where previously it could hit unexpected sleeps, trigger warnings.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>

With the changelog clarified
Acked-by: Michal Hocko <mhocko@...e.com>
Thanks!

> ---
>  mm/vmalloc.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 6dbcdceecae1..81b6d3bde719 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2017,6 +2017,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	unsigned long freed;
>  	unsigned long addr;
>  	unsigned int vn_id;
> +	bool allow_block;
>  	int purged = 0;
>  	int ret;
>  
> @@ -2026,7 +2027,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	if (unlikely(!vmap_initialized))
>  		return ERR_PTR(-EBUSY);
>  
> -	might_sleep();
> +	allow_block = gfpflags_allow_blocking(gfp_mask);
> +	might_sleep_if(allow_block);
>  
>  	/*
>  	 * If a VA is obtained from a global heap(if it fails here)
> @@ -2065,8 +2067,16 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	 * If an allocation fails, the error value is
>  	 * returned. Therefore trigger the overflow path.
>  	 */
> -	if (IS_ERR_VALUE(addr))
> -		goto overflow;
> +	if (IS_ERR_VALUE(addr)) {
> +		if (allow_block)
> +			goto overflow;
> +
> +		/*
> +		 * We can not trigger any reclaim logic because
> +		 * sleeping is not allowed, thus fail an allocation.
> +		 */
> +		goto error;
> +	}
>  
>  	va->va_start = addr;
>  	va->va_end = addr + size;
> @@ -2116,6 +2126,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  		pr_warn("vmalloc_node_range for size %lu failed: Address range restricted to %#lx - %#lx\n",
>  				size, vstart, vend);
>  
> +error:
>  	kmem_cache_free(vmap_area_cachep, va);
>  	return ERR_PTR(-EBUSY);
>  }
> -- 
> 2.39.5

-- 
Michal Hocko
SUSE Labs