[merged] watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug.patch removed from -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     Subject: kernel/watchdog.c: avoid races between /proc handlers and CPU hotplug
has been removed from the -mm tree.  Its filename was
     watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Acked-by: Don Zickus <dzickus@xxxxxxxxxx>
Reviewed-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/watchdog.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff -puN kernel/watchdog.c~watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug kernel/watchdog.c
--- a/kernel/watchdog.c~watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug
+++ a/kernel/watchdog.c
@@ -857,6 +857,7 @@ static int proc_watchdog_common(int whic
 	int err, old, new;
 	int *watchdog_param = (int *)table->data;
 
+	get_online_cpus();
 	mutex_lock(&watchdog_proc_mutex);
 
 	if (watchdog_suspended) {
@@ -908,6 +909,7 @@ static int proc_watchdog_common(int whic
 	}
 out:
 	mutex_unlock(&watchdog_proc_mutex);
+	put_online_cpus();
 	return err;
 }
 
@@ -949,6 +951,7 @@ int proc_watchdog_thresh(struct ctl_tabl
 {
 	int err, old;
 
+	get_online_cpus();
 	mutex_lock(&watchdog_proc_mutex);
 
 	if (watchdog_suspended) {
@@ -974,6 +977,7 @@ int proc_watchdog_thresh(struct ctl_tabl
 	}
 out:
 	mutex_unlock(&watchdog_proc_mutex);
+	put_online_cpus();
 	return err;
 }
 
@@ -988,6 +992,7 @@ int proc_watchdog_cpumask(struct ctl_tab
 {
 	int err;
 
+	get_online_cpus();
 	mutex_lock(&watchdog_proc_mutex);
 
 	if (watchdog_suspended) {
@@ -1015,6 +1020,7 @@ int proc_watchdog_cpumask(struct ctl_tab
 	}
 out:
 	mutex_unlock(&watchdog_proc_mutex);
+	put_online_cpus();
 	return err;
 }
 
_

Patches currently in -mm which might be from uobergfe@xxxxxxxxxx are


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