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

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Date: Thu, 9 May 2024 16:06:36 +0800
From: Hailong Liu <hailong.liu@...o.com>
To: Michal Hocko <mhocko@...e.com>
CC: <akpm@...ux-foundation.org>, <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 Thu, 09. May 09:48, Michal Hocko wrote:
> On Wed 08-05-24 20:58:08, 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>
> > ---
> >  mm/vmalloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 6641be0ca80b..2f359d08bf8d 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3560,7 +3560,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >
> >  	/* High-order pages or fallback path if "bulk" fails. */
> >  	while (nr_allocated < nr_pages) {
> > -		if (fatal_signal_pending(current))
> > +		if (!(gfp & __GFP_NOFAIL) && fatal_signal_pending(current))
>
> Use nofail instead of gfp & __GFP_NOFAIL.
>
> Other than that looks good to me. After that is fixed, please feel free
> to add Acked-by: Michal Hocko <mhocko@...e.com>
>
> I believe this should also have Fixes: 9376130c390a ("mm/vmalloc: add support for __GFP_NOFAIL")
> --
> Michal Hocko
> SUSE Labs

Thanks for the review and the Ack!

Add Fixes in V2 patch.

IIUC, nofail could not used for this case.

	/*
	 * For order-0 pages we make use of bulk allocator, if
	 * the page array is partly or not at all populated due
	 * to fails, fallback to a single page allocator that is
	 * more permissive.
	 */
	if (!order) {
		/* bulk allocator doesn't support nofail req. officially */
		xxx
-> nofail = false;
	} else if (gfp & __GFP_NOFAIL) {
		/*
		 * Higher order nofail allocations are really expensive and
		 * potentially dangerous (pre-mature OOM, disruptive reclaim
		 * and compaction etc.
		 */
		alloc_gfp &= ~__GFP_NOFAIL;
		nofail = true;
	}

	/* High-order pages or fallback path if "bulk" fails. */
	while (nr_allocated < nr_pages) {

-> nofail is false here if bulk allocator fails.
		if (fatal_signal_pending(current))
			break;

--

Best Regards,
Hailong.