On Thu, Jan 12, 2023 at 03:56:29PM +0800, Zqiang wrote:
> Currently, the start_poll_synchronize_rcu_expedited() can be invoked
> very early. before rcu_init(), the rcu_data structure's->mynode is not
> initialized, if invoke start_poll_synchronize_rcu_expedited() before
> rcu_init(), will trigger a null rcu_node structure's->exp_seq_poll access.
>
> This commit add boot_exp_seq_poll_rq member to rcu_state structure to
> store seq number return by invoke start_poll_synchronize_rcu_expedited()
> very early.
>
> Fixes: d96c52fe4907 ("rcu: Add polled expedited grace-period primitives")
> Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Just a nit below:
> ---
> kernel/rcu/tree.c | 3 ++-
> kernel/rcu/tree.h | 1 +
> kernel/rcu/tree_exp.h | 6 ++++--
> 3 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 63545d79da51..12f0891ce7f4 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -92,6 +92,7 @@ static struct rcu_state rcu_state = {
> .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
> .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
> .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
> + .boot_exp_seq_poll_rq = RCU_GET_STATE_COMPLETED,
> };
>
> /* Dump rcu_node combining tree at boot to verify correct setup. */
> @@ -4938,7 +4939,7 @@ void __init rcu_init(void)
> 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))
> + if (!(rcu_state.boot_exp_seq_poll_rq & 0x1))
This can be "if (!(rcu_state.boot_exp_seq_poll_rq == RCU_GET_STATE_COMPLETED))"
> (void)start_poll_synchronize_rcu_expedited();
>
> rcu_test_sync_prims();
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index 192536916f9a..ae50ca6853ad 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -397,6 +397,7 @@ struct rcu_state {
> /* Synchronize offline with */
> /* GP pre-initialization. */
> int nocb_is_setup; /* nocb is setup from boot */
> + unsigned long boot_exp_seq_poll_rq;
A comment on the right can mention: "/* exp seq poll request before rcu_init() */"
Thanks!
> };
>
> /* Values for rcu_state structure's gp_flags field. */
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index 956cd459ba7f..1b35a1e233d9 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -1068,9 +1068,11 @@ 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);
> + } else
> + rcu_state.boot_exp_seq_poll_rq = s;
> }
> if (rcu_init_invoked())
> raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
> --
> 2.25.1
>
