On 5/31/2024 4:03 AM, Andrew Morton wrote:
> 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.
>
> What are the userspace-visible runtime effects of this change?
>
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index d12a17fc0c17..869e7788a7d5 100644
>> --- 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.
>
> That patch didn't describe the runtime effects either.
>
> Folks, please always do this. So that others can decide whether their
> kernel needs the fix, and so that others can decide whether this fix
> might address an issue which their users are reporting.
Thanks for suggestion. I send v2 in
https://lore.kernel.org/lkml/20240531024820.5507-1-hailong.liu@xxxxxxxx/T/#u
I promise to make my future commit messages comprehensive, in order to help others.
Brs,
Hailong.
