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    Subject[PATCH tip/core/rcu 22/24] rcu: Make RCU able to tolerate undefined CONFIG_RCU_KTHREAD_PRIO
    Date
    From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

    This commit updates the initialization of the kthread_prio boot parameter
    so that RCU will build even when CONFIG_RCU_KTHREAD_PRIO is undefined.
    The kthread_prio boot parameter is set to CONFIG_RCU_KTHREAD_PRIO if
    that is defined, otherwise to 1 if CONFIG_RCU_BOOST is defined and
    to zero otherwise. This commit then makes CONFIG_RCU_KTHREAD_PRIO
    depend on CONFIG_RCU_EXPERT, so that Kconfig users won't be asked about
    CONFIG_RCU_KTHREAD_PRIO unless they want to be.

    Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
    Reported-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
    ---
    init/Kconfig | 1 +
    kernel/rcu/tree.c | 4 ++++
    2 files changed, 5 insertions(+)

    diff --git a/init/Kconfig b/init/Kconfig
    index 78176001f73b..af2c93c4a105 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -671,6 +671,7 @@ config RCU_KTHREAD_PRIO
    range 0 99 if !RCU_BOOST
    default 1 if RCU_BOOST
    default 0 if !RCU_BOOST
    + depends on RCU_EXPERT
    help
    This option specifies the SCHED_FIFO priority value that will be
    assigned to the rcuc/n and rcub/n threads and is also the value
    diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    index 960054da4ae5..0ab9e711a649 100644
    --- a/kernel/rcu/tree.c
    +++ b/kernel/rcu/tree.c
    @@ -160,7 +160,11 @@ static void invoke_rcu_core(void);
    static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);

    /* rcuc/rcub kthread realtime priority */
    +#ifdef CONFIG_RCU_KTHREAD_PRIO
    static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
    +#else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */
    +static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
    +#endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */
    module_param(kthread_prio, int, 0644);

    /* Delay in jiffies for grace-period initialization delays, debug only. */
    --
    1.8.1.5


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