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Subject[tip:core/urgent] watchdog/core: Rework CPU hotplug locking
Commit-ID:  b7a349819d4b9b5db64e523351e66a79a758eaa5
Gitweb: http://git.kernel.org/tip/b7a349819d4b9b5db64e523351e66a79a758eaa5
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 12 Sep 2017 21:37:00 +0200
Committer: Ingo Molnar <mingo@kernel.org>
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@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>
---
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;
}

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