[to-be-updated] watchdog-core-fix-aa-deadlock-due-to-watchdog-holding-cpu_hotplug_lock-and-wait-for-wq.patch removed from -mm tree

[to-be-updated] watchdog-core-fix-aa-deadlock-due-to-watchdog-holding-cpu_hotplug_lock-and-wait-for-wq.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: watchdog/core: fix AA deadlock due to watchdog holding cpu_hotplug_lock and wait for wq
has been removed from the -mm tree.  Its filename was
     watchdog-core-fix-aa-deadlock-due-to-watchdog-holding-cpu_hotplug_lock-and-wait-for-wq.patch

This patch was dropped because an updated version will be merged

------------------------------------------------------
From: Luo Gengkun <luogengkun@huaweicloud.com>
Subject: watchdog/core: fix AA deadlock due to watchdog holding cpu_hotplug_lock and wait for wq
Date: Thu, 6 Jun 2024 15:38:28 +0000

We found an AA deadlock problem as shown belowed:

TaskA				TaskB				WatchDog			system_wq

...
css_killed_work_fn:
P(cgroup_mutex)
...
								...
								__lockup_detector_reconfigure:
								P(cpu_hotplug_lock.read)
								...
				...
				cpu_up:
				percpu_down_write:
				P(cpu_hotplug_lock.write)
												...
												cgroup_bpf_release:
												P(cgroup_mutex)
								smp_call_on_cpu:
								Wait system_wq

cpuset_css_offline:
P(cpu_hotplug_lock.read)

WatchDog is waiting for system_wq, who is waitting for cgroup_mutex, to
finish the jobs, but the owner of the cgroup_mutex is waitting for
cpu_hotplug_lock.  The key point is the cpu_hotplug_lock, cause the
system_wq may be waitting other lock.  It seems unhealthy to hold a lock
when waitting system_wq, because we never know what jobs are system_wq
doing.  So I fix this by replace cpu_read_lock/unlock with
cpu_hotplug_disable/enable to prevent cpu offline/online.

Link: https://lkml.kernel.org/r/20240606153828.3261006-1-luogengkun@huaweicloud.com
Fixes: e31d6883f21c ("watchdog/core, powerpc: Lock cpus across reconfiguration")
Signed-off-by: Luo Gengkun <luogengkun@huaweicloud.com>
Cc: Bitao Hu <yaoma@linux.alibaba.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/watchdog.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/watchdog.c~watchdog-core-fix-aa-deadlock-due-to-watchdog-holding-cpu_hotplug_lock-and-wait-for-wq
+++ a/kernel/watchdog.c
@@ -867,7 +867,7 @@ int lockup_detector_offline_cpu(unsigned
 
 static void __lockup_detector_reconfigure(void)
 {
-	cpus_read_lock();
+	cpu_hotplug_disable();
 	watchdog_hardlockup_stop();
 
 	softlockup_stop_all();
@@ -877,7 +877,7 @@ static void __lockup_detector_reconfigur
 		softlockup_start_all();
 
 	watchdog_hardlockup_start();
-	cpus_read_unlock();
+	cpu_hotplug_enable();
 	/*
 	 * Must be called outside the cpus locked section to prevent
 	 * recursive locking in the perf code.
@@ -916,11 +916,11 @@ static __init void lockup_detector_setup
 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
 static void __lockup_detector_reconfigure(void)
 {
-	cpus_read_lock();
+	cpu_hotplug_disable();
 	watchdog_hardlockup_stop();
 	lockup_detector_update_enable();
 	watchdog_hardlockup_start();
-	cpus_read_unlock();
+	cpu_hotplug_enable();
 }
 void lockup_detector_reconfigure(void)
 {
_

Patches currently in -mm which might be from luogengkun@huaweicloud.com are