Re: [RFC PATCH] mm/vmalloc: fix vbq->free breakage

[Andrew Morton]

On Thu, 30 May 2024 17:31:08 +0800 <hailong.liu@xxxxxxxx> wrote:

> From: "hailong.liu" <hailong.liu@xxxxxxxx>
> 
> The function xa_for_each() in _vm_unmap_aliases() loops through all
> vbs. However, since commit 062eacf57ad9 ("mm: vmalloc: remove a global
> vmap_blocks xarray") the vb from xarray may not be on the corresponding
> CPU vmap_block_queue. Consequently, purge_fragmented_block() might
> use the wrong vbq->lock to protect the free list, leading to vbq->free
> breakage.
> 
> ...
>
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2269,10 +2269,9 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
>  	for_each_possible_cpu(cpu) {
>  		struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, cpu);
>  		struct vmap_block *vb;
> -		unsigned long idx;
> 
>  		rcu_read_lock();
> -		xa_for_each(&vbq->vmap_blocks, idx, vb) {
> +		list_for_each_entry_rcu(vb, &vbq->free, free_list) {
>  			spin_lock(&vb->lock);
> 
>  			/*
> ---
> https://lore.kernel.org/all/20240530025144.1570865-1-zhaoyang.huang@xxxxxxxxxx/
> BTW, zhangyang also encounter the same issue, maybe revert commit not a
> better solution. we need a map to get vbq from vb.

I borrowed the Fixes: from that patch and added cc:stable, pending
confirmation that the runtime effects are significant.