[tip:core/urgent] watchdog/core: Rework CPU hotplug locking

[tip-bot for Thomas Gleixner]

Commit-ID:  b7a349819d4b9b5db64e523351e66a79a758eaa5
Gitweb:     http://git.kernel.org/tip/b7a349819d4b9b5db64e523351e66a79a758eaa5
Author:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Tue, 12 Sep 2017 21:37:00 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 14 Sep 2017 11:41:04 +0200

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@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sebastian Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170912194146.568079057@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/watchdog.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index b2d4675..cd79f64 100644
--- 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;
 }