linux-kernel - Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP

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Date: Wed, 8 May 2024 22:43:21 +0800
From: Hailong Liu <hailong.liu@...o.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
CC: <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.com>,
	<urezki@...il.com>, <hch@...radead.org>, <lstoakes@...il.com>,
	<21cnbao@...il.com>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<xiang@...nel.org>, <chao@...nel.org>, Oven <liyangouwen1@...o.com>
Subject: Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if
 called with __GFP_NOFAIL

On Wed, 08. May 21:41, Gao Xiang wrote:
>
> +Cc Michal,
>
> On 2024/5/8 20:58, hailong.liu@...o.com wrote:
> > From: "Hailong.Liu" <hailong.liu@...o.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@...o.com>
> > Signed-off-by: Hailong.Liu <hailong.liu@...o.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.