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SubjectRe: [PATCH 2/3] mm/memory_hotplug: harden try_offline_node against bogus nid
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On 06.07.20 03:19, Jia He wrote:
> When testing the remove_memory path of dax pmem, there will be a panic with
> call trace:
> try_remove_memory+0x84/0x170
> remove_memory+0x38/0x58
> dev_dax_kmem_remove+0x3c/0x84 [kmem]
> device_release_driver_internal+0xfc/0x1c8
> device_release_driver+0x28/0x38
> bus_remove_device+0xd4/0x158
> device_del+0x160/0x3a0
> unregister_dev_dax+0x30/0x68
> devm_action_release+0x20/0x30
> release_nodes+0x150/0x240
> devres_release_all+0x6c/0x1d0
> device_release_driver_internal+0x10c/0x1c8
> driver_detach+0xac/0x170
> bus_remove_driver+0x64/0x130
> driver_unregister+0x34/0x60
> dax_pmem_exit+0x14/0xffc4 [dax_pmem]
> __arm64_sys_delete_module+0x18c/0x2d0
> el0_svc_common.constprop.2+0x78/0x168
> do_el0_svc+0x34/0xa0
> el0_sync_handler+0xe0/0x188
> el0_sync+0x164/0x180
>
> It is caused by the bogus nid (-1). Although the root cause is pmem dax
> translates from pxm to node_id incorrectly due to numa_off, it is worth
> hardening the codes in try_offline_node(), quiting if !pgdat.
>
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
> mm/memory_hotplug.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index da374cd3d45b..e1e290577b45 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1680,6 +1680,9 @@ void try_offline_node(int nid)
> pg_data_t *pgdat = NODE_DATA(nid);
> int rc;
>
> + if (WARN_ON(!pgdat))
> + return;
> +
> /*
> * If the node still spans pages (especially ZONE_DEVICE), don't
> * offline it. A node spans memory after move_pfn_range_to_zone(),
>

Hm. If I am not wrong, somebody used add_memory() with another nid than
try_remove_memory()?

Or did we pass the node_possible(nid) check in add_memory_resource(),
and succeeded to add to nid==-1?

Having that said, this feels somewhat wrong, especially checking against
pgdat down in try_offline_node(). It really has to be the same nid as
used when adding - and that nid has to be sane.

--
Thanks,

David / dhildenb

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