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 <b...@alien8.de> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Cc: Don Zickus <dzic...@redhat.com> Cc: Chris Metcalf <cmetc...@mellanox.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Sebastian Siewior <bige...@linutronix.de> Cc: Nicholas Piggin <npig...@gmail.com> Cc: Ulrich Obergfell <uober...@redhat.com> Cc: Andrew Morton <a...@linux-foundation.org> Link: http://lkml.kernel.org/r/20170831073053.437818...@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; }
