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rcu: Set rcutree.kthread_prio sysfs access to read-only 

The rcutree.kthread_prio kernel-boot parameter is used to set the
priority for boost (rcub), per-CPU (rcuc), and grace-period (rcu_preempt
or rcu_sched) kthreads.  It is also used by rcutorture to check whether
it is possible to meaningfully test RCU priority boosting.  However,
all of these cases will either ignore or be confused by any post-boot
changes to rcutree.kthread_prio.

Note that the user really can change the priorities of all of these
kthreads using chrt, given sufficient privileges.  Therefore, the
read-write nature of sysfs access to rcutree.kthread_prio is thus at
best an attractive nuisance.

This commit therefore changes sysfs access to rcutree.kthread_prio to
be read-only.

Signed-off-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Liu Song 2019-02-21 22:13:27 +08:00 committed by Paul E. McKenney
parent 884157cef0
commit 3ffe3d1adc
1 changed files with 1 additions and 1 deletions
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2
kernel/rcu/tree.c
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@ -149,7 +149,7 @@ static void sync_sched_exp_online_cleanup(int cpu);
/* rcuc/rcub kthread realtime priority */
static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
module_param(kthread_prio, int, 0644);
module_param(kthread_prio, int, 0444);
/* Delay in jiffies for grace-period initialization delays, debug only. */