Re: [PATCH v2 8/9] perf/cxl: Don't use pmu.dev in IRQ and hotplug callbacks after unregister

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 29 Jul 2026 07:55:54 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> On device removal the devm actions unwind LIFO, so cxl_pmu_perf_unregister()
> runs first and perf_pmu_unregister() frees info->pmu.dev (device_del() +
> put_device() -> kfree()). The overflow IRQ (freed last) and the CPU-hotplug
> instance (removed next) are still live at that point, and both
> cxl_pmu_irq() and cxl_pmu_offline_cpu() log via dev_dbg()/dev_err() on
> info->pmu.dev, dereferencing freed memory. The shared IRQ can be entered
> for a co-function on the same MSI vector, and a CPU can go offline in the
> window before the hotplug instance is removed.
> 
> Log through info->pmu.parent instead, the cxl_pmu device passed to probe,
> which is devm-managed and outlives every teardown action.
> 
> Fixes: 5d7107c72796 ("perf: CXL Performance Monitoring Unit driver")
> Reported-by: sashiko-bot@kernel.org
> Closes: https://sashiko.dev/#/patchset/20260715191454.459673-1-dave@stgolabs.net?part=1
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>

In general logging on subsystem devices is flakey so

Acked-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

> ---
>  drivers/perf/cxl_pmu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/perf/cxl_pmu.c b/drivers/perf/cxl_pmu.c
> index 2e817a52ff1e..f42238b2b6b0 100644
> --- a/drivers/perf/cxl_pmu.c
> +++ b/drivers/perf/cxl_pmu.c
> @@ -803,7 +803,7 @@ static irqreturn_t cxl_pmu_irq(int irq, void *data)
>  		struct perf_event *event = info->hw_events[i];
>  
>  		if (!event) {
> -			dev_dbg(info->pmu.dev,
> +			dev_dbg(info->pmu.parent,
>  				"overflow but on non enabled counter %d\n", i);
>  			continue;
>  		}
> @@ -966,7 +966,7 @@ static int cxl_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
>  	info->on_cpu = -1;
>  	target = cpumask_any_but(cpu_online_mask, cpu);
>  	if (target >= nr_cpu_ids) {
> -		dev_err(info->pmu.dev, "Unable to find a suitable CPU\n");
> +		dev_err(info->pmu.parent, "Unable to find a suitable CPU\n");
>  		return 0;
>  	}
>