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Subject[patch 06/29] lockup_detector: Rework cpu hotplug locking
The watchdog proc interface causes extensive recursive locking of the cpu
hotplug percpu rwsem, which is deadlock prone.

Replace the get/put_online_cpus() pairs with cpu_hotplug_disable()/enable()
calls for now. Later patches will remove that requirement completely.

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/watchdog.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -703,7 +703,7 @@ static int proc_watchdog_common(int whic
int err, old, new;
int *watchdog_param = (int *)table->data;

- get_online_cpus();
+ cpu_hotplug_disable();
mutex_lock(&watchdog_proc_mutex);

/*
@@ -752,7 +752,7 @@ static int proc_watchdog_common(int whic
}
out:
mutex_unlock(&watchdog_proc_mutex);
- put_online_cpus();
+ cpu_hotplug_enable();
return err;
}

@@ -794,7 +794,7 @@ int proc_watchdog_thresh(struct ctl_tabl
{
int err, old, new;

- get_online_cpus();
+ cpu_hotplug_disable();
mutex_lock(&watchdog_proc_mutex);

old = ACCESS_ONCE(watchdog_thresh);
@@ -818,7 +818,7 @@ int proc_watchdog_thresh(struct ctl_tabl
}
out:
mutex_unlock(&watchdog_proc_mutex);
- put_online_cpus();
+ cpu_hotplug_enable();
return err;
}

@@ -833,7 +833,7 @@ int proc_watchdog_cpumask(struct ctl_tab
{
int err;

- get_online_cpus();
+ cpu_hotplug_disable();
mutex_lock(&watchdog_proc_mutex);

err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
@@ -856,7 +856,7 @@ int proc_watchdog_cpumask(struct ctl_tab
}

mutex_unlock(&watchdog_proc_mutex);
- put_online_cpus();
+ cpu_hotplug_enable();
return err;
}


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