[v3] dma-buf: dma-heap: Add a size check for allocation

From: Guangming <Guangming.Cao@mediatek.com>

Add a size check for allocation since the allocation size is
always less than the total DRAM size.

Without this check, once the invalid size allocation runs on a process that
can't be killed by OOM flow(such as "gralloc" on Android devices), it will
cause a kernel exception, and to make matters worse, we can't find who are using
so many memory with "dma_buf_debug_show" since the relevant dma-buf hasn't exported.

To make OOM issue easier, maybe need dma-buf framework to dump the buffer size
under allocating in "dma_buf_debug_show".

Signed-off-by: Guangming <Guangming.Cao@mediatek.com>
Signed-off-by: jianjiao zeng <jianjiao.zeng@mediatek.com>
---
v3: 1. update patch, use right shift to replace division.
    2. update patch, add reason in code and commit message.
v2: 1. update size limitation as total_dram page size.
    2. update commit message
---
 drivers/dma-buf/dma-heap.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

On Fri, Jan 14, 2022 at 4:04 AM Guangming.Cao
<guangming.cao@mediatek.com> wrote:
>
> On Fri, 2022-01-14 at 08:16 +0100, Christian König wrote:
> > Am 14.01.22 um 00:26 schrieb John Stultz:
> > > On Thu, Jan 13, 2022 at 5:05 AM Christian König
> > > <christian.koenig@amd.com> wrote:
> > > > Am 13.01.22 um 14:00 schrieb Ruhl, Michael J:
> > > > > > -----Original Message-----
> > > > > > From: dri-devel <dri-devel-bounces@lists.freedesktop.org> On
> > > > > > Behalf Of
> > > > > > Ruhl, Michael J
> > > > > > > -----Original Message-----
> > > > > > > From: dri-devel <dri-devel-bounces@lists.freedesktop.org>
> > > > > > > On Behalf Of
> > > > > > > guangming.cao@mediatek.com
> > > > > > > +   /*
> > > > > > > +    * Invalid size check. The "len" should be less than
> > > > > > > totalram.
> > > > > > > +    *
> > > > > > > +    * Without this check, once the invalid size allocation
> > > > > > > runs on a process
> > > > > > > that
> > > > > > > +    * can't be killed by OOM flow(such as "gralloc" on
> > > > > > > Android devices), it
> > > > > > > will
> > > > > > > +    * cause a kernel exception, and to make matters worse,
> > > > > > > we can't find
> > > > > > > who are using
> > > > > > > +    * so many memory with "dma_buf_debug_show" since the
> > > > > > > relevant
> > > > > > > dma-buf hasn't exported.
> > > > > > > +    */
> > > > > > > +   if (len >> PAGE_SHIFT > totalram_pages())
> > > > > >
> > > > > > If your "heap" is from cma, is this still a valid check?
> > > > >
> > > > > And thinking a bit further, if I create a heap from something
> > > > > else (say device memory),
> > > > > you will need to be able to figure out the maximum allowable
> > > > > check for the specific
> > > > > heap.
> > > > >
> > > > > Maybe the heap needs a callback for max size?
> Yes, I agree with this solution.
> If dma-heap framework support this via adding a callback to support it,
> seems it's more clear than adding a limitation in dma-heap framework
> since each heap maybe has different limitation.
> If you prefer adding callback, I can update this patch and add totalram
> limitation to system dma-heap.

If the max value is per-heap, why not enforce that value in the
per-heap allocation function?

Moving the check to the heap alloc to me seems simpler to me than
adding complexity to the infrastructure to add a heap max_size
callback. Is there some other use for the callback that you envision?

thanks
-john

On Wed, Jan 19, 2022 at 1:58 AM Guangming.Cao
<guangming.cao@mediatek.com> wrote:
> On Fri, 2022-01-14 at 17:17 -0800, John Stultz wrote:
> > If the max value is per-heap, why not enforce that value in the
> > per-heap allocation function?
> >
> > Moving the check to the heap alloc to me seems simpler to me than
> > adding complexity to the infrastructure to add a heap max_size
> > callback. Is there some other use for the callback that you envision?
> >
>
> If you think max the value is per-heap, why not add an optional
> callback for dma-heap to solve this issue(prevent consuming too much
> time for a doomed to fail allocation), if the dma-heap doesn't have a
> special size check, just use the default value(totalram) in dma-heap
> framework to do the size check.

As the totalram default isn't correct for all heaps (or necessarily
even most heaps), so those heaps would need to implement the callback.

I'm just not sure adding complexity to the framework to address this
is useful. Instead of an additional check in the allocation function,
heap implementers will need to assess if the default logic in a
framework is correct, and then possibly implement the callback.

> Yes, for linux dma-heaps, only system-heap needs it, so adding it in
> system heap is the simplest. However, there are many vendor dma-heaps
> like system-heap which won't be uploaded to linux codebase, and maybe
> have same limitation, all these heaps need to add the same limitation.

My worry is that without seeing these vendor heaps, this is a bit of a
theoretical concern. We don't have the data on how common this is.
I very much hope that vendors can start submitting their heaps
upstream (along with drivers that benefit from the heaps). Then we can
really assess what makes the most sense for the community maintained
code.


> I just think it's boring. However, If you think discussing these absent
> cases based on current linux code is meaningless, I also agree to it.

So, as a rule, the upstream kernel doesn't create/maintain logic to
accommodate out of tree code.

Now, I agree there is the potential for some duplication in the checks
in the allocation logic, but until it affects the upstream kernel,
community maintainers can't really make an appropriate evaluation.

As a contra-example, if the allocation is some extreme hotpath, adding
an extra un-inlinable function pointer traversal for the size callback
may actually have a negative impact. This isn't likely but again, if
we cannot demonstrate it one way or the other against the upstream
tree, we can't figure out what the best solution might be.


> So, to summarize, if you still think adding it in system_heap.c is
> better, I also agree and I will update the patch to add it in
> system_heap.c

I think this is the best solution for now. As this is not part of an
userland ABI, we can always change it in the future once we see the
need.

thanks
-john