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rcu: Make rcu_gp_kthread() check for early-boot activity

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The rcu_gp_kthread() function immediately sleeps waiting to be notified
of the need for a new grace period, which currently works because there
are a number of code sequences that will provide the needed wakeup later.
However, some of these code sequences need to acquire the root rcu_node
structure's ->lock, and contention on that lock has started manifesting.
This commit therefore makes rcu_gp_kthread() check for early-boot activity
when it starts up, omitting the initial sleep in that case.

Reported-by: Nicholas Piggin <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Tested-by: Nicholas Piggin <[email protected]>
This commit is contained in:
Paul E. McKenney 2018-04-11 16:41:20 -07:00
commit 5fe0a56298
1 changed files with 6 additions and 0 deletions
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6
kernel/rcu/tree.c
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@ -2192,6 +2192,12 @@ static int __noreturn rcu_gp_kthread(void *arg)
struct rcu_state *rsp = arg;
struct rcu_node *rnp = rcu_get_root(rsp);
/* Check for early-boot work. */
raw_spin_lock_irq_rcu_node(rnp);
if (need_any_future_gp(rnp))
WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
raw_spin_unlock_irq_rcu_node(rnp);
rcu_bind_gp_kthread();
for (;;) {