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Date: Mon, 22 Apr 2024 18:38:57 +0800
From: Hailong Liu <hailong.liu@oppo.com>
To: Barry Song <21cnbao@gmail.com>
CC: <akpm@linux-foundation.org>, <urezki@gmail.com>, <hch@infradead.org>,
	<lstoakes@gmail.com>, <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v2] mm/vmalloc: fix return value of vb_alloc if size
 is 0.
Message-ID: <20240422103857.qw5mrcnj4rgej2jh@oppo.com>
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On Mon, 22. Apr 11:46, Barry Song wrote:
> On Fri, Apr 19, 2024 at 6:17 PM <hailong.liu@oppo.com> wrote:
> >
> > From: "Hailong.Liu" <hailong.liu@oppo.com>
> >
> > vm_map_ram check return value of vb_alloc by IS_ERR. if
> > vm_map_ram(page, 0, 0) , vb_alloc(0, GFP_KERNEL) would return NULL
> > which cause kernel panic by vmap_pages_range_noflush。fix this by
> > return ERR_PTR(-EINVAL) if size is 0.
> >
> > Signed-off-by: Hailong.Liu <hailong.liu@oppo.com>
> > ---
> > Changes since v1 [1]:
> > - Return ERR_PTR(-EINVAL) or not check IS_ERR_OR_NULL
> >
> > BTW,  Barry suggests me that if count is 0, return directly, in my
> > opinion, change return value is more resonable.
> >
> > [1] https://lore.kernel.org/all/84d7cd03-1cf8-401a-8edf-2524db0bd6d5@oppo.com/
> >
> >  mm/vmalloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index a3fedb3ee0db..c430a999805b 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2173,7 +2173,7 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
> >                  * get_order(0) returns funny result. Just warn and terminate
> >                  * early.
> >                  */
> > -               return NULL;
> > +               return ERR_PTR(-EINVAL);
>
> might be ZERO_SIZE_PTR.

Hi Barry,
Hi Barry, I use ERR_PTR(-EINVAL) to keep consistency with the return
value of the function alloc_vmap_area.

	if (unlikely(!size || offset_in_page(size) || !is_power_of_2(align)))
		return ERR_PTR(-EINVAL);

IMO, ZERO_SIZE_PTR is used by slab and can not be catched by IS_ERR().

--
Best Regards,
Hailong.