On Wed, Dec 01, 2021 at 07:26:43PM -0800, Andrew Morton wrote:
> On Thu, 2 Dec 2021 10:06:24 +0800 Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx> wrote:
>
> > Delete the WARN_ON() and return NULL directly for oversized parameter
> > in kvmalloc() calls.
> > Also add unlikely().
> >
> > Fixes: 7661809d493b ("mm: don't allow oversized kvmalloc() calls")
> > Signed-off-by: Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx>
> > ---
> > There are a lot of oversize warnings and patches about kvmalloc() calls
> > recently. Maybe these warnings are not very necessary.
>
> Or maybe they are. Please let's take a look at these warnings, one at
> a time. If a large number of them are bogus then sure, let's disable
> the runtime test. But perhaps it's the case that calling code has
> genuine issues and should be repaired.
Andrew,
The problem is that this WARN_ON() is triggered by the users.
At least in the RDMA world, users can provide huge sizes and they expect
to get plain -ENOMEM and not dump stack, because it happens indirectly
to them.
In our case, these two kvcalloc() generates WARN_ON().
umem_odp->pfn_list = kvcalloc(
npfns, sizeof(*umem_odp->pfn_list), GFP_KERNEL);
if (!umem_odp->pfn_list)
return -ENOMEM;
umem_odp->dma_list = kvcalloc(
ndmas, sizeof(*umem_odp->dma_list), GFP_KERNEL);
https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/infiniband/core/umem_odp.c#L80
It is not a kernel programmer error to allow "oversized kvmalloc call" .
Thanks
