Re: [PATCH] PCI: Warn about host bridge device when its numa node is NO_NODE

[Michal Hocko <mhocko@kernel.org>]

On Wed 23-10-19 12:10:39, Bjorn Helgaas wrote:
> On Wed, Oct 23, 2019 at 04:22:43PM +0800, Yunsheng Lin wrote:
> > On 2019/10/23 5:04, Bjorn Helgaas wrote:
> > > On Sat, Oct 19, 2019 at 02:45:43PM +0800, Yunsheng Lin wrote:
> 
> > > I think the underlying problem you're addressing is that:
> > > 
> > >   - NUMA_NO_NODE == -1,
> > >   - dev_to_node(dev) may return NUMA_NO_NODE,
> > >   - kmalloc(dev) relies on cpumask_of_node(dev_to_node(dev)), and
> > >   - cpumask_of_node(NUMA_NO_NODE) makes an invalid array reference
> > > 
> > > For example, on arm64, mips loongson, s390, and x86,
> > > cpumask_of_node(node) returns "node_to_cpumask_map[node]", and -1 is
> > > an invalid array index.
> > 
> > The invalid array index of -1 is the underlying problem here when
> > cpumask_of_node(dev_to_node(dev)) is called and cpumask_of_node()
> > is not NUMA_NO_NODE aware yet.
> > 
> > In the "numa: make node_to_cpumask_map() NUMA_NO_NODE aware" thread
> > disscusion, it is requested that it is better to warn about the pcie
> > device without a node assigned by the firmware before making the
> > cpumask_of_node() NUMA_NO_NODE aware, so that the system with pci
> > devices of "NUMA_NO_NODE" node can be fixed by their vendor.
> > 
> > See: https://lore.kernel.org/lkml/20191011111539.GX2311@hirez.programming.kicks-ass.net/
> 
> Right.  We should warn if the NUMA node number would help us but DT or
> the firmware didn't give us one.
> 
> But we can do that independently of any cpumask_of_node() changes.
> There's no need to do one patch before the other.  Even if you make
> cpumask_of_node() tolerate NUMA_NO_NODE, we'll still get the warning
> because we're not actually changing any node assignments.

Agreed. And this has been proposed previously I believe but my
understanding was that Petr was against that.

-- 
Michal Hocko
SUSE Labs