[2/3] srcu: Explain the reason behind the read side critical section on GP start
Commit Message
Tell about the need to protect against concurrent updaters who may
overflow the GP counter behind the current update.
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
kernel/rcu/srcutree.c | 5 +++++
1 file changed, 5 insertions(+)
@@ -1154,6 +1154,11 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
int ss_state;
check_init_srcu_struct(ssp);
+ /*
+ * While starting the new gp if needed, make sure we are in an SRCU read
+ * side critical section so that the gp sequence can't wrap around in
+ * the middle.
+ */
idx = __srcu_read_lock_nmisafe(ssp, false);
ss_state = smp_load_acquire(&ssp->srcu_size_state);
if (ss_state < SRCU_SIZE_WAIT_CALL)