Re: [PATCH v2] drivers/base/memory: set mem->altmap after successful device registration

[Richard Cheng <icheng@nvidia.com>]

On Thu, May 14, 2026 at 02:26:57AM +0800, Georgi Djakov wrote:
> If __add_memory_block() fails at xa_store() (under memory pressure
> for example), device_unregister() is called, which eventually
> triggers memory_block_release() with mem->altmap still set, causing
> a WARN_ON(mem->altmap). This was triggered by modifying virtio-mem
> driver.
>

I see you mentioned about some out of tree virtio_mem patches that
can trigger the bug, mind to paste the tree link here ?
Just curious.

Best regards,
Richard Cheng.
 
> Fix this by delaying the assignment of mem->altmap until after
> __add_memory_block() has succeeded.
> 
> Fixes: 1a8c64e11043 ("mm/memory_hotplug: embed vmem_altmap details in memory block")
> Signed-off-by: Georgi Djakov <georgi.djakov@oss.qualcomm.com>
> ---
> 
> v1: https://patch.msgid.link/20260513130900.2204499-1-georgi.djakov@oss.qualcomm.com
> 
>  drivers/base/memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 11d57cfa8d72..78e9600e6d45 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -807,7 +807,6 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
>  	mem->start_section_nr = block_id * sections_per_block;
>  	mem->state = state;
>  	mem->nid = nid;
> -	mem->altmap = altmap;
>  	INIT_LIST_HEAD(&mem->group_next);
>  
>  #ifndef CONFIG_NUMA
> @@ -825,6 +824,8 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
>  	if (ret)
>  		return ret;
>  
> +	mem->altmap = altmap;
> +
>  	if (group) {
>  		mem->group = group;
>  		list_add(&mem->group_next, &group->memory_blocks);
>