linux-kernel - Re: [PATCH 2/2] mm: vmalloc: Replace BUG_ON() by WARN_ON

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Date:   Tue, 20 Dec 2022 18:53:18 +0000
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 2/2] mm: vmalloc: Replace BUG_ON() by WARN_ON_ONCE()

On Tue, Dec 20, 2022 at 07:27:04PM +0100, Uladzislau Rezki (Sony) wrote:
> Currently a vm_unmap_ram() functions triggers a BUG() if an area
> is not found. Replace it by the WARN_ON_ONCE() error message and
> keep machine alive instead of stopping it.
>
> The worst case is a memory leaking.
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  mm/vmalloc.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 0fc38c36e0df..e05a0dc79ac5 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2255,10 +2255,12 @@ void vm_unmap_ram(const void *mem, unsigned int count)
>  	}
>
>  	va = find_unlink_vmap_area(addr);
> -	BUG_ON(!va);
> -	debug_check_no_locks_freed((void *)va->va_start,
> -				    (va->va_end - va->va_start));
> -	free_unmap_vmap_area(va);
> +
> +	if (!WARN_ON_ONCE(!va)) {
> +		debug_check_no_locks_freed((void *)va->va_start,
> +			(va->va_end - va->va_start));
> +		free_unmap_vmap_area(va);
> +	}
>  }
>  EXPORT_SYMBOL(vm_unmap_ram);
>
> --
> 2.30.2
>

Absolutely in favour of this in principle (BUG_ON() is something we should
resort to in only the direst of circumstances), one small nit - perhaps it'd be
neater to simply make this a guard clause? E.g.:-

	if (!WARN_ON_ONCE(!va))
		return;

	...