linux-kernel - Re: [RFC PATCH v2 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

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Message-ID: <aQopoAj3i2jdIX6V@pc636>
Date: Tue, 4 Nov 2025 17:28:16 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Uladzislau Rezki <urezki@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH v2 1/4] mm/vmalloc: warn on invalid vmalloc gfp flags

On Mon, Nov 03, 2025 at 11:04:26AM -0800, Vishal Moola (Oracle) wrote:
> Vmalloc explicitly supports a list of flags, but we never enforce them.
> vmalloc has been trying to handle unsupported flags by clearing and
> setting flags wherever necessary. This is messy and makes the code
> harder to understand, when we could simply check for a supported input
> immediately instead.
> 
> Define a helper mask and function telling callers they have passed in
> invalid flags, and clear those unsupported vmalloc flags.
> 
> Suggested-by: Christoph Hellwig <hch@...radead.org>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> ---
>  mm/vmalloc.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 0832f944544c..290016c7fb58 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3911,6 +3911,26 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  	return NULL;
>  }
>  
> +/*
> + * See __vmalloc_node_range() for a clear list of supported vmalloc flags.
> + * This gfp lists all flags currently passed through vmalloc. Currently,
> + * __GFP_ZERO is used by BFP and __GFP_NORETRY is used by percpu.
> + */
> +#define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\
> +				__GFP_NOFAIL |  __GFP_ZERO | __GFP_NORETRY)
> +
> +static gfp_t vmalloc_fix_flags(gfp_t flags)
> +{
> +	gfp_t invalid_mask = flags & ~GFP_VMALLOC_SUPPORTED;
> +
> +	flags &= GFP_VMALLOC_SUPPORTED;
> +	pr_warn("Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n",
> +			invalid_mask, &invalid_mask, flags, &flags);
> +	dump_stack();
>
WARN_ON() or friends? It prints the stack.

> +
> +	return flags;
> +}
> +
>  /**
>   * __vmalloc_node_range - allocate virtually contiguous memory
>   * @size:		  allocation size
> @@ -4092,6 +4112,8 @@ EXPORT_SYMBOL_GPL(__vmalloc_node_noprof);
>  
>  void *__vmalloc_noprof(unsigned long size, gfp_t gfp_mask)
>  {
> +	if (gfp_mask & ~GFP_VMALLOC_SUPPORTED)
> +		gfp_mask = vmalloc_fix_flags(gfp_mask);
>  	return __vmalloc_node_noprof(size, 1, gfp_mask, NUMA_NO_NODE,
>  				__builtin_return_address(0));
>  }
> @@ -4131,6 +4153,8 @@ EXPORT_SYMBOL(vmalloc_noprof);
>   */
>  void *vmalloc_huge_node_noprof(unsigned long size, gfp_t gfp_mask, int node)
>  {
> +	if (gfp_mask & ~GFP_VMALLOC_SUPPORTED)
> +		gfp_mask = vmalloc_fix_flags(gfp_mask);
>
gfp_mask = check_and_fix_flags()? 

--
Uladzislau Rezki