Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP_NOFAIL

Hailong Liu
2024-05-08T14:43:34Z

On Wed, 08. May 21:41, Gao Xiang wrote:
>
> +Cc Michal,
>
> On 2024/5/8 20:58, hailong.liu@oppo.com wrote:
> > From: "Hailong.Liu" <hailong.liu@oppo.com>
> >
> > Commit a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc")
> > includes support for __GFP_NOFAIL, but it presents a conflict with
> > commit dd544141b9eb ("vmalloc: back off when the current task is
> > OOM-killed"). A possible scenario is as belows:
> >
> > process-a
> > kvcalloc(n, m, GFP_KERNEL | __GFP_NOFAIL)
> > __vmalloc_node_range()
> > __vmalloc_area_node()
> > vm_area_alloc_pages()
> > --> oom-killer send SIGKILL to process-a
> > if (fatal_signal_pending(current)) break;
> > --> return NULL;
> >
> > to fix this, do not check fatal_signal_pending() in vm_area_alloc_pages()
> > if __GFP_NOFAIL set.
> >
> > Reported-by: Oven <liyangouwen1@oppo.com>
> > Signed-off-by: Hailong.Liu <hailong.liu@oppo.com>
>
> Why taging this as RFC here? It seems a corner-case fix of
> commit a421ef303008
>
> Thanks,
> Gao Xiang
>

Hi Gao Xiang:

RFC here to wait for a better way to handle this case :).
IMO, if vmalloc support __GFP_NOFAIL it should not return
null even system is deadlock on memory.

--

Best Regards,
Hailong.