Re: [PATCH] cxl/port: Fix decoder initialization when nr_targets > interleave_ways

[Dave Jiang <dave.jiang@intel.com>]

On 12/21/23 23:12, Dan Williams wrote:
> From: Huang Ying <ying.huang@intel.com>
> 
> The decoder_populate_targets() helper walks all of the targets in a port
> and makes sure they can be looked up in @target_map. Where @target_map
> is a lookup table from target position to target id (corresponding to a
> cxl_dport instance). However @target_map is only responsible for
> conveying the active dport instances as conveyed by interleave_ways.
> 
> When nr_targets > interleave_ways it results in
> decoder_populate_targets() walking off the end of the valid entries in
> @target_map. Given target_map is initialized to 0 it results in the
> dport lookup failing if position 0 is not mapped to a dport with an id
> of 0:
> 
>   cxl_port port3: Failed to populate active decoder targets
>   cxl_port port3: Failed to add decoder
>   cxl_port port3: Failed to add decoder3.0
>   cxl_bus_probe: cxl_port port3: probe: -6
> 
> This bug also highlights that when the decoder's ->targets[] array is
> written in cxl_port_setup_targets() it is missing a hold of the
> targets_lock to synchronize against sysfs readers of the target list. A
> fix for that is saved for a later patch.
> 
> Fixes: a5c258021689 ("cxl/bus: Populate the target list at decoder create")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> [djbw: rewrite the changelog, find the Fixes: tag]
> Co-developed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/cxl/core/port.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index b7c93bb18f6e..57495cdc181f 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1644,7 +1644,7 @@ static int decoder_populate_targets(struct cxl_switch_decoder *cxlsd,
>  		return -EINVAL;
>  
>  	write_seqlock(&cxlsd->target_lock);
> -	for (i = 0; i < cxlsd->nr_targets; i++) {
> +	for (i = 0; i < cxlsd->cxld.interleave_ways; i++) {
>  		struct cxl_dport *dport = find_dport(port, target_map[i]);
>  
>  		if (!dport) {
> 
>