From 7f8714f5d1d1e510de451f17ec2e44bde458e891 Mon Sep 17 00:00:00 2001
From: Petr Pavlu <petr.pavlu@suse.com>
Date: Fri, 17 Mar 2023 11:36:01 +0100
Subject: [PATCH] Revert "mei: me: enable asynchronous probing"
Patch-mainline: Never, a workaround to avoid a more intrusive fix
References: bsc#1208048, bsc#1209126

This reverts upstream commit 67de6bf1e4f869a490656448f471fdc4a0a405ad.

The following scenario can occur during system boot on machines that
have PCI devices requiring modules intel_lpss_pci and mei_me:
* A systemd-udevd task starts loading intel_lpss_pci. Its init function
  registers a new driver which gets matched with a PCI device. The code
  takes a lock on the device plus on its parent (__driver_attach() ->
  device_driver_attach()), and invokes the probe function of the driver
  intel_lpss_pci_probe().
* The probe requests a load of module idma64. A modprobe task is spawned
  for that. Initialization of this module is successful but the module
  loader code waits before returning on all async work to complete:
  do_init_module() -> async_synchronize_full() ->
  async_synchronize_full_domain() -> async_synchronize_cookie_domain().
* Concurrently to intel_lpss_pci, the mei_me module gets loaded. This
  driver allows async probing which is handled by
  __driver_attach_async_helper() and run on a kworker task. The function
  tries to probe a matched PCI device which requires taking a lock on
  the device and its parent, but finds that the parent is already locked
  by systemd-udevd and so sleeps.
* Result is a deadlock where the systemd-udevd task holds the PCI bus
  lock and indirectly waits on all async work to complete (through
  request_module()), but the async worker probing the mei_me device on
  the bus cannot proceed because it requires the same PCI lock.

The issue has been fixed upstream effectively by 8c97a46af04b ("driver
core: hold dev's parent lock when needed") but that patch breaks kABI
and cannot be easily backported.

Use of async probing is limited on SLE12-SP5. As an alternative, disable
this method again for mei_me too in order to avoid the described issue.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
---
 drivers/misc/mei/pci-me.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/misc/mei/pci-me.c b/drivers/misc/mei/pci-me.c
index 5bf0d50d55a0..fb470c3e0466 100644
--- a/drivers/misc/mei/pci-me.c
+++ b/drivers/misc/mei/pci-me.c
@@ -523,7 +523,6 @@ static struct pci_driver mei_me_driver = {
 	.remove = mei_me_remove,
 	.shutdown = mei_me_shutdown,
 	.driver.pm = MEI_ME_PM_OPS,
-	.driver.probe_type = PROBE_PREFER_ASYNCHRONOUS,
 };
 
 module_pci_driver(mei_me_driver);
-- 
2.35.3