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rcu: Permit start_poll_synchronize_rcu_expedited() to be invoked early

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According to the commit log of the patch that added it to the kernel,
start_poll_synchronize_rcu_expedited() can be invoked very early, as
in long before rcu_init() has been invoked.  But before rcu_init(),
the rcu_data structure's ->mynode field has not yet been initialized.
This means that the start_poll_synchronize_rcu_expedited() function's
attempt to set the CPU's leaf rcu_node structure's ->exp_seq_poll_rq
field will result in a segmentation fault.

This commit therefore causes start_poll_synchronize_rcu_expedited() to
set ->exp_seq_poll_rq only after rcu_init() has initialized all CPUs'
rcu_data structures' ->mynode fields.  It also removes the check from
the rcu_init() function so that start_poll_synchronize_rcu_expedited(
is unconditionally invoked.  Yes, this might result in an unnecessary
boot-time grace period, but this is down in the noise.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
This commit is contained in:
Zqiang 2023-01-12 10:48:29 -08:00 committed by Joel Fernandes (Google)
parent 46103fe01b
commit 7ea91307ad
2 changed files with 5 additions and 5 deletions
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5
kernel/rcu/tree.c
View file

@ -4942,9 +4942,8 @@ void __init rcu_init(void)
else
qovld_calc = qovld;
// Kick-start any polled grace periods that started early.
if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))
(void)start_poll_synchronize_rcu_expedited();
// Kick-start in case any polled grace periods started early.
(void)start_poll_synchronize_rcu_expedited();
rcu_test_sync_prims();
}

5
kernel/rcu/tree_exp.h
View file

@ -1066,9 +1066,10 @@ unsigned long start_poll_synchronize_rcu_expedited(void)
if (rcu_init_invoked())
raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
if (!poll_state_synchronize_rcu(s)) {
rnp->exp_seq_poll_rq = s;
if (rcu_init_invoked())
if (rcu_init_invoked()) {
rnp->exp_seq_poll_rq = s;
queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
}
}
if (rcu_init_invoked())
raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);