kernel/watchdog.c: avoid races between /proc handlers and CPU hotplug
The handler functions for watchdog parameters in /proc/sys/kernel do not protect themselves against races with CPU hotplug. Hence, theoretically it is possible that a new watchdog thread is started on a hotplugged CPU while a parameter is being modified, and the thread could thus use a parameter value that is 'in transition'. For example, if 'watchdog_thresh' is being set to zero (note: this disables the lockup detectors) the thread would erroneously use the value zero as the sample period. To avoid such races and to keep the /proc handler code consistent, call {get|put}_online_cpus() in proc_watchdog_common() {get|put}_online_cpus() in proc_watchdog_thresh() {get|put}_online_cpus() in proc_watchdog_cpumask() Signed-off-by: Ulrich Obergfell <uobergfe@redhat.com> Acked-by: Don Zickus <dzickus@redhat.com> Reviewed-by: Aaron Tomlin <atomlin@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -857,6 +857,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
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int err, old, new;
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int *watchdog_param = (int *)table->data;
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get_online_cpus();
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mutex_lock(&watchdog_proc_mutex);
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if (watchdog_suspended) {
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@ -908,6 +909,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
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}
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out:
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mutex_unlock(&watchdog_proc_mutex);
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put_online_cpus();
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return err;
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}
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@ -949,6 +951,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
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{
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int err, old;
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get_online_cpus();
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mutex_lock(&watchdog_proc_mutex);
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if (watchdog_suspended) {
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@ -974,6 +977,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
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}
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out:
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mutex_unlock(&watchdog_proc_mutex);
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put_online_cpus();
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return err;
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}
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@ -988,6 +992,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
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{
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int err;
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get_online_cpus();
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mutex_lock(&watchdog_proc_mutex);
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if (watchdog_suspended) {
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@ -1015,6 +1020,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
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}
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out:
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mutex_unlock(&watchdog_proc_mutex);
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put_online_cpus();
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return err;
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}
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