From de3f2671ae563d24c679dcca36c9e0ebd9564ebd Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 2 Aug 2022 11:59:49 -0700 Subject: [PATCH] srcu: Make Tiny SRCU poll_state_synchronize_srcu() more precise This commit applies the more-precise grace-period-state check used by rcu_seq_done_exact() to poll_state_synchronize_srcu(). This is important because Tiny SRCU uses a 16-bit counter, which can wrap quite quickly. If counter wrap continues to be a problem, then expanding ->srcu_idx and ->srcu_idx_max to 32 bits might be warranted. Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutiny.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index 92c002d65482..a2af24f21467 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -240,10 +240,10 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); */ bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) { - bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie); + unsigned short cur_s = READ_ONCE(ssp->srcu_idx); barrier(); - return ret; + return USHORT_CMP_GE(cur_s, cookie) || USHORT_CMP_LT(cur_s, cookie - 3); } EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);