linux-kernel - Re: PROBLEM: kernel crashes when running xfsdump since ~6.4

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Date: Wed, 26 Jun 2024 09:34:44 -0400
From: Nick Bowler <nbowler@...conx.ca>
To: Uladzislau Rezki <urezki@...il.com>
Cc: Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
 Linux regressions mailing list <regressions@...ts.linux.dev>,
 linux-mm@...ck.org, sparclinux@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Hailong Liu <hailong.liu@...o.com>
Subject: Re: PROBLEM: kernel crashes when running xfsdump since ~6.4

On 2024-06-26 06:51, Uladzislau Rezki wrote:
[...]
> Thank you for pointing this. Below is updated version with extra comment:

I checked that I can still reproduce the problem on 6.10-rc5 and with
this patch applied on top, xfsdump doesn't crash anymore.

> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 45e1506d58c3..03b82fb8ecd3 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2542,7 +2542,15 @@ static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue);
>  static struct xarray *
>  addr_to_vb_xa(unsigned long addr)
>  {
> -	int index = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus();
> +	int index = (addr / VMAP_BLOCK_SIZE) % nr_cpu_ids;
> +
> +	/*
> +	 * Please note, nr_cpu_ids points on a highest set
> +	 * possible bit, i.e. we never invoke cpumask_next()
> +	 * if an index points on it which is nr_cpu_ids - 1.
> +	 */
> +	if (!cpu_possible(index))
> +		index = cpumask_next(index, cpu_possible_mask);
>  
>  	return &per_cpu(vmap_block_queue, index).vmap_blocks;
>  }

Thanks,
  Nick