From ae3c0706160b60ac5e7d36aac428ae6e572dc932 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 13 Oct 2022 19:22:43 +0200 Subject: srcu: Explain the reason behind the read side critical section on GP start Tell about the need to protect against concurrent updaters who may overflow the GP counter behind the current update. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'kernel/rcu/srcutree.c') diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 18bb696cff8c..272830a87e56 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1158,6 +1158,11 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, int ss_state; check_init_srcu_struct(ssp); + /* + * While starting a new grace period, make sure we are in an + * SRCU read-side critical section so that the grace-period + * sequence number cannot wrap around in the meantime. + */ idx = __srcu_read_lock_nmisafe(ssp, false); ss_state = smp_load_acquire(&ssp->srcu_size_state); if (ss_state < SRCU_SIZE_WAIT_CALL) -- cgit v1.2.3