Re: [PATCH] nouveau/dmem: handle kcalloc() allocation failure

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 05 Mar 2024, duoming@zju.edu.cn wrote:
> On Mon, 04 Mar 2024 14:14:52 +0200 Jani Nikula wrote:
>> >> The kcalloc() in nouveau_dmem_evict_chunk() will return null if
>> >> the physical memory has run out. As a result, if we dereference
>> >> src_pfns, dst_pfns or dma_addrs, the null pointer dereference bugs
>> >> will happen.
>> >>
>> >> This patch uses stack variables to replace the kcalloc().
>> >
>> > Won't this blow the stack?  And why not just test the return value of
>> > kcalloc?
>> 
>> VLAs should not be used in the kernel anymore. Building this results in
>> a warning due to -Wvla. See 0bb95f80a38f ("Makefile: Globally enable VLA
>> warning").
>> 
>> Error checking and propagation is the way to go.
>
> The GPU is going away. If the kcalloc() in nouveau_dmem_evict_chunk() fail,
> we could not evict all pages mapping a chunk. Do you think we should add a
> __GFP_NOFAIL flag in kcalloc()? I see the __GFP_NOFAIL flag is used in the
> following code:
>
> /*
> * _GFP_NOFAIL because the GPU is going away and there
> * is nothing sensible we can do if we can't copy the
> * data back.
> */
> dpage = alloc_page(GFP_HIGHUSER | __GFP_NOFAIL);

This is all up to the nouveau maintainers, really. All I'm saying is
that VLA isn't the solution you're looking for.

BR,
Jani.


-- 
Jani Nikula, Intel