Re: [PATCH] dma-buf/heaps: c9e8440eca61 staging: ion: Fix overflow and list bugs in system heap:

["T.J. Mercier" <tjmercier@google.com>]

On Tue, Mar 28, 2023 at 8:13 PM Jaewon Kim <jaewon31.kim@samsung.com> wrote:
>
> >On Tue, Mar 28, 2023 at 5:58?AM Jaewon Kim <jaewon31.kim@samsung.com> wrote:
> >>
> >> Normal free:212600kB min:7664kB low:57100kB high:106536kB
> >>   reserved_highatomic:4096KB active_anon:276kB inactive_anon:180kB
> >>   active_file:1200kB inactive_file:0kB unevictable:2932kB
> >>   writepending:0kB present:4109312kB managed:3689488kB mlocked:2932kB
> >>   pagetables:13600kB bounce:0kB free_pcp:0kB local_pcp:0kB
> >>   free_cma:200844kB
> >> Out of memory and no killable processes...
> >> Kernel panic - not syncing: System is deadlocked on memory
> >>
> >> An OoM panic was reported, there were only native processes which are
> >> non-killable as OOM_SCORE_ADJ_MIN.
> >>
> >> After looking into the dump, I've found the dma-buf system heap was
> >> trying to allocate a huge size. It seems to be a signed negative value.
> >>
> >> dma_heap_ioctl_allocate(inline)
> >>     |  heap_allocation = 0xFFFFFFC02247BD38 -> (
> >>     |    len = 0xFFFFFFFFE7225100,
> >>
> >> Actually the old ion system heap had policy which does not allow that
> >> huge size with commit c9e8440eca61 ("staging: ion: Fix overflow and list
> >> bugs in system heap"). We need this change again. Single allocation
> >> should not be bigger than half of all memory.
> >>
> >> Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
> >> ---
> >>  drivers/dma-buf/heaps/system_heap.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> >> index e8bd10e60998..4c1ef2ecfb0f 100644
> >> --- a/drivers/dma-buf/heaps/system_heap.c
> >> +++ b/drivers/dma-buf/heaps/system_heap.c
> >> @@ -351,6 +351,9 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
> >>         struct page *page, *tmp_page;
> >>         int i, ret = -ENOMEM;
> >>
> >> +       if (len / PAGE_SIZE > totalram_pages() / 2)
> >> +               return ERR_PTR(-ENOMEM);
> >> +
> >
> >Instead of policy like that, would __GFP_RETRY_MAYFAIL on the system
> >heap's LOW_ORDER_GFP flags also avoid the panic, and eventually fail
> >the allocation request?
>
> Hello T.J.
>
> Thank you for your opinion.
> The __GFP_RETRY_MAYFAIL on LOW_ORDER_GFP seems to work.
>
> page allocation failure: order:0, mode:0x144dc2(GFP_HIGHUSER|__GFP_RETRY_MAYFAIL|__GFP_COMP|__GFP_ZERO)
> Node 0 active_anon:120kB inactive_anon:43012kB active_file:36kB inactive_file:788kB
>
> I tried to test it, and the allocation stopped at very low file cache situation without OoM panic
> as we expected. The phone device was freezing for few seconds though.
>
> We can avoid OoM panic through either totalram_pages() / 2 check or __GFP_RETRY_MAYFAIL.
>
> But I think we still need the totalram_pages() / 2 check so that we don't have to suffer
> the freezing in UX perspective. We may kill some critical processes or users' recent apps.
>
> Regarding __GFP_RETRY_MAYFAIL, I think it will help us avoid OoM panic. But I'm worried
> about low memory devices which still need OoM kill to get memory like in camera scenarios.
>
> So what do you think?
>
Hey Jaewon, thanks for checking! The totalram_pages() / 2 just feels
somewhat arbitrary. On the lowest memory devices I'm aware of that use
the system heap it would take a single buffer on the order of several
hundred megabytes to exceed that, so I guess the simple check is fine
here until someone says they just can't live without a buffer that
big!

Reviewed-by: T.J. Mercier <tjmercier@google.com>