Commit c21357e4 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Neeraj Upadhyay (AMD)
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srcu: Explain why callbacks invocations can't run concurrently 



If an SRCU barrier is queued while callbacks are running and a new
callbacks invocator for the same sdp were to run concurrently, the
RCU barrier might execute too early. As this requirement is non-obvious,
make sure to keep a record.

Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarNeeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>
parent 94c55b9e

kernel/rcu/srcutree.c

+6 −0
Original line number Diff line number Diff line
@@ -1715,6 +1715,11 @@ static void srcu_invoke_callbacks(struct work_struct *work) 
	WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));

	rcu_segcblist_advance(&sdp->srcu_cblist,

			      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));

	/*

	 * Although this function is theoretically re-entrant, concurrent

	 * callbacks invocation is disallowed to avoid executing an SRCU barrier

	 * too early.

	 */

	if (sdp->srcu_cblist_invoking ||

	    !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {

		spin_unlock_irq_rcu_node(sdp);
@@ -1745,6 +1750,7 @@ static void srcu_invoke_callbacks(struct work_struct *work) 
	sdp->srcu_cblist_invoking = false;

	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);

	spin_unlock_irq_rcu_node(sdp);

	/* An SRCU barrier or callbacks from previous nesting work pending */

	if (more)

		srcu_schedule_cbs_sdp(sdp, 0);

}