Re: [PATCH 2/3] powerpc/powernv: fix preempt count leak in pnv_kexec_wait_secondaries_down

[Shrikanth Hegde]

Hi Aboorva.

On 5/18/26 10:38 AM, Aboorva Devarajan wrote:

pnv_kexec_wait_secondaries_down() calls get_cpu() to obtain the current
CPU id but never calls the matching put_cpu(), leaking one
preempt_disable() nesting level on every invocation.

In practice the imbalance does not trigger a visible splat because the
kexec teardown path is a one-way trip: IRQs are already disabled, no
schedule() occurs after the leak, and default_machine_kexec() overwrites
preempt_count with HARDIRQ_OFFSET before jumping into kexec_sequence()
which never returns. However the bookkeeping is still wrong.

In the kexec teardown path IRQs are already disabled and the CPU is
pinned, so get_cpu()'s preempt_disable() side-effect is unnecessary.
Replace get_cpu() with raw_smp_processor_id() which returns the CPU id
without touching preempt_count.

Fixes: 298b34d7d578 ("powerpc/powernv: Fix kexec races going back to OPAL")
Signed-off-by: Aboorva Devarajan <aboor...@linux.ibm.com>
---
  arch/powerpc/platforms/powernv/setup.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/setup.c 
b/arch/powerpc/platforms/powernv/setup.c
index 4dbb47ddbdcc4..177da0defcb36 100644
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c
@@ -396,7 +396,7 @@ static void pnv_kexec_wait_secondaries_down(void)
  {
        int my_cpu, i, notified = -1;

- my_cpu = get_cpu();

+       my_cpu = raw_smp_processor_id();

Is it always with irq-disabled?
How about !CONFIG_SMP and in kexec_prepare_cpus. I see it disables interrupt 
later.
(though it is a less common config)

So use smp_processor_id()?? One could compile with CONFIG_DEBUG_PREEMPT=y and
see any reports.

        for_each_online_cpu(i) {
                uint8_t status;