[PATCH] mailbox: pcc: Free the channel before unmapping the shared memory

[Breno Leitao <leitao@debian.org>]

I am seeing a crash on PCC that is related to a an shared memory being
unmapped before the IRQ is disabled, and the IRQ kicks in and hits the
unmapped (NULL) address. This is a summary of what I see on my box:

	scmi_protocol scmi_dev.1: Message for 1 type 0 is not expected!
	Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
	 __handle_irq_event_percpu+0x1c4/0x9e0
	 handle_irq_event+0x98/0x218
	 handle_fasteoi_irq+0x230/0x750
	 generic_handle_domain_irq+0xac/0x138
	 gic_handle_irq+0x344/0x740
	 call_on_irq_stack+0x30/0x48

The trapping store is iowrite32(SCMI_SHMEM_FLAG_INTR_ENABLED,
&shmem->header.flags), a write of 1 at offset 4 of a NULL base.

But, back to the problem, pcc_mbox_free_channel() unmaps the shared
memory and clears pchan->chan.shmem *before* freeing the IRQ (aka
calling mbox_free_channel()).

The interrupt is still live when the mapping goes away.

Free the channel first, before the memory unmap. mbox_free_channel()
calls pcc_shutdown(), which frees the platform interrupt, and then unmap
shared memory.

Fixes: 7f9e19f207be ("mailbox: pcc: Check before sending MCTP PCC response ACK")
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/mailbox/pcc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index 636879ae1db76..d32f170141de7 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -408,12 +408,13 @@ void pcc_mbox_free_channel(struct pcc_mbox_chan *pchan)
 		return;
 	pchan_info = chan->con_priv;
 	pcc_mbox_chan = &pchan_info->chan;
+
+	mbox_free_channel(chan);
+
 	if (pcc_mbox_chan->shmem) {
 		iounmap(pcc_mbox_chan->shmem);
 		pcc_mbox_chan->shmem = NULL;
 	}
-
-	mbox_free_channel(chan);
 }
 EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);
 

---
base-commit: 5e6de6a2b522f659defacb1551d0465ba6ce13cf
change-id: 20260812-pcc-3a7413982a5e

Best regards,
--  
Breno Leitao <leitao@debian.org>