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

Hailong Liu
2024-05-09T08:21:49Z

On Thu, 09. May 09:48, Michal Hocko wrote:
> On Wed 08-05-24 20:58:08, 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>
> > ---
> > 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@suse.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.