Commit 8a77f38b authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

srcu: Only accelerate on enqueue time 



Acceleration in SRCU happens on enqueue time for each new callback. This
operation is expected not to fail and therefore any similar attempt
from other places shouldn't find any remaining callbacks to accelerate.

Moreover accelerations performed beyond enqueue time are error prone
because rcu_seq_snap() then may return the snapshot for a new grace
period that is not going to be started.

Remove these dangerous and needless accelerations and introduce instead
assertions reporting leaking unaccelerated callbacks beyond enqueue
time.

Co-developed-by: default avatarYong He <alexyonghe@tencent.com>
Signed-off-by: default avatarYong He <alexyonghe@tencent.com>
Co-developed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Co-developed-by: default avatarNeeraj upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: default avatarNeeraj upadhyay <Neeraj.Upadhyay@amd.com>
Reviewed-by: default avatarLike Xu <likexu@tencent.com>
Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
parent 4a8e65b0

kernel/rcu/srcutree.c

+2 −4
Original line number Diff line number Diff line
@@ -784,8 +784,7 @@ static void srcu_gp_start(struct srcu_struct *ssp) 
	spin_lock_rcu_node(sdp);  /* Interrupts already disabled. */

	rcu_segcblist_advance(&sdp->srcu_cblist,

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

	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,

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

	WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));

	spin_unlock_rcu_node(sdp);  /* Interrupts remain disabled. */

	WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies);

	WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0);
@@ -1721,6 +1720,7 @@ static void srcu_invoke_callbacks(struct work_struct *work) 
	ssp = sdp->ssp;

	rcu_cblist_init(&ready_cbs);

	spin_lock_irq_rcu_node(sdp);

	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));

	if (sdp->srcu_cblist_invoking ||
@@ -1750,8 +1750,6 @@ static void srcu_invoke_callbacks(struct work_struct *work) 
	 */

	spin_lock_irq_rcu_node(sdp);

	rcu_segcblist_add_len(&sdp->srcu_cblist, -len);

	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,

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

	sdp->srcu_cblist_invoking = false;

	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);

	spin_unlock_irq_rcu_node(sdp);