Re: [PATCH v2] dax/kmem: account for partial dis-contiguous resource upon removal

[Alison Schofield]

On Mon, Feb 23, 2026 at 12:15:16PM -0800, Davidlohr Bueso wrote:
> When dev_dax_kmem_probe() partially succeeds (at least one range
> is mapped) but a subsequent range fails request_mem_region()
> or add_memory_driver_managed(), the probe silently continues,
> ultimately returning success, but with the corresponding range
> resource NULL'ed out.
> 
> dev_dax_kmem_remove() iterates over all dax_device ranges regardless
> of if the underlying resource exists. When remove_memory() is
> called later, it returns 0 because the memory was never added which
> causes dev_dax_kmem_remove() to incorrectly assume the (nonexistent)
> resource can be removed and attempts cleanup on a NULL pointer.

Do you have a failure signature w Call Trace to paste here?
If not, maybe just insert the expected signature for grepping:
"BUG: unable to handle kernel NULL pointer dereference"

Reviewed-by: Alison Schofield <alison.schofield@xxxxxxxxx>

> 
> Fix this by skipping these ranges altogether, noting that these
> cases are considered success, such that the cleanup is still
> reached when all actually-added ranges are successfully removed.
> 
> Reviewed-by: Ben Cheatham <benjamin.cheatham@xxxxxxx>
> Fixes: 60e93dc097f7 ("device-dax: add dis-contiguous resource support")
> Signed-off-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> ---
> Changes from v1: reword some of the changelog (Ben)
> 
>  drivers/dax/kmem.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index c036e4d0b610..edd62e68ffb7 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -227,6 +227,12 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  		if (rc)
>  			continue;
>  
> +		/* range was never added during probe */
> +		if (!data->res[i]) {
> +			success++;
> +			continue;
> +		}
> +
>  		rc = remove_memory(range.start, range_len(&range));
>  		if (rc == 0) {
>  			remove_resource(data->res[i]);
> -- 
> 2.39.5
> 
>