Commit ee5e2448 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Explain srcu_funnel_gp_start() call to list_add() is safe 



This commit adds a comment explaining why an unprotected call to
list_add() from srcu_funnel_gp_start() can be safe.  TL;DR: It is only
called during very early boot when we don't have no steeking concurrency!

Co-developed-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 46470cf8

kernel/rcu/srcutree.c

+6 −0
Original line number Diff line number Diff line
@@ -776,6 +776,12 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, 
	    rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {

		WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));

		srcu_gp_start(ssp);



		// And how can that list_add() in the "else" clause

		// possibly be safe for concurrent execution?  Well,

		// it isn't.  And it does not have to be.  After all, it

		// can only be executed during early boot when there is only

		// the one boot CPU running with interrupts still disabled.

		if (likely(srcu_init_done))

			queue_delayed_work(rcu_gp_wq, &ssp->work,

					   srcu_get_delay(ssp));