Re: [PATCH rdma-next] RDMA/core: Silence oversized kvmalloc() warning

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Mar 31, 2025 at 10:04:05PM +0300, Leon Romanovsky wrote:
> 
> 
> On Mon, Mar 31, 2025, at 20:45, Jason Gunthorpe wrote:
> > On Wed, Mar 26, 2025 at 12:58:54PM +0200, Leon Romanovsky wrote:
> >> On Wed, Mar 19, 2025 at 02:23:49PM -0300, Jason Gunthorpe wrote:
> >> > On Wed, Mar 19, 2025 at 02:42:21PM +0200, Leon Romanovsky wrote:
> >> > > From: Shay Drory <shayd@nvidia.com>
> >> > > 
> >> > > syzkaller triggered an oversized kvmalloc() warning.
> >> > > Silence it by adding __GFP_NOWARN.
> >> > 
> >> > I don't think GFP_NOWARN is the right thing..
> >> > 
> >> > We've hit this before and I think we ended up adding a size limit
> >> > check prior to the kvmalloc to prevent the overflow triggered warning.
> >> 
> >> The size check was needed before this commit was merged:
> >> 0708a0afe291 ("mm: Consider __GFP_NOWARN flag for oversized kvmalloc() calls")
> >> 
> >> From that point, the correct solution is simply provide __GFP_NOWARN flag.
> >
> > I'm not sure, NOWARN removes all warnings, even normal OOM warnings
> > from regually sized allocations which we don't want to remove.
> 
> I disagree, this allocation is called from user space. We can safely
> skip OOM messages and error here will be enough.

That is not the standard, we OOM splat on all userspace allocations
too.

GFP_NOWARN is supposed to be used in cases where the OOM has a
recovery and nothing will fail.

I think the right thing here is to limit the size, though I'm not
really sure what the limit should be.

Jason