Re: [PATCH] cxl/mbox: Break poison list loop on an empty payload

On Thu, Jul 09, 2026 at 08:57:14AM -0700, Dave Jiang wrote:
> A device that returns count == 0 with CXL_POISON_FLAG_MORE set on every
> iteration never advances nr_records, so the max_errors guard never
> trips and the do/while loops forever while holding poison.mutex. That
> hangs the sysfs-triggered scan thread and blocks all subsequent poison
> operations on the device. The existing "Protect against an uncleared
> _FLAG_MORE" guard was intended to bound a misbehaving device but does
> not cover the count == 0 case.
> 
> Stop the loop on an empty payload so a malfunctioning or malicious
> device cannot wedge the poison scan.


I'm guessing Sashiko's new pre-existing complaint will appear as
a new patch in the future, so for this one, let's get it merged:

Reviewed-by: Alison Schofield <[email protected]>


> 
> Link: https://sashiko.dev/#/patchset/[email protected]?part=3
> Fixes: ed83f7ca398b ("cxl/mbox: Add GET_POISON_LIST mailbox command")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Dave Jiang <[email protected]>
> ---
>  drivers/cxl/core/mbox.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 7c6c5b7450a5..c09fae2cae9f 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -1455,6 +1455,11 @@ int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len,
>  		if (rc)
>  			break;
>  
> +		if (!le16_to_cpu(po->count)) {
> +			dev_dbg(&cxlmd->dev, "Poison empty payload!\n");
> +			break;
> +		}
> +
>  		for (int i = 0; i < le16_to_cpu(po->count); i++)
>  			trace_cxl_poison(cxlmd, cxlr, &po->record[i],
>  					 po->flags, po->overflow_ts,
> 
> base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
> -- 
> 2.54.0
>