watchdog/core: 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>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194146.568079057@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index b2d4675..cd79f64 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -703,7 +703,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
        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 which, struct ctl_table *table, int write,
        }
 out:
        mutex_unlock(&watchdog_proc_mutex);
-       put_online_cpus();
+       cpu_hotplug_enable();
        return err;
 }
 
@@ -794,7 +794,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
 {
        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_table *table, int write,
        }
 out:
        mutex_unlock(&watchdog_proc_mutex);
-       put_online_cpus();
+       cpu_hotplug_enable();
        return err;
 }
 
@@ -833,7 +833,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
 {
        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_table *table, int write,
        }
 
        mutex_unlock(&watchdog_proc_mutex);
-       put_online_cpus();
+       cpu_hotplug_enable();
        return err;
 }