Commit 3116a32e authored by Valentin Schneider's avatar Valentin Schneider Committed by Neeraj Upadhyay
Browse files

rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_snap_stopped_since() 



The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
RCU_WATCHING, the dynticks prefix can go.

While at it, this helper is only meant to be called after failing an
earlier call to rcu_watching_snap_in_eqs(), document this in the comments
and add a WARN_ON_ONCE() for good measure.

Signed-off-by: default avatarValentin Schneider <vschneid@redhat.com>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarNeeraj Upadhyay <neeraj.upadhyay@kernel.org>
parent 9629936d

Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst

+1 −1
Original line number Diff line number Diff line
@@ -150,7 +150,7 @@ This case is handled by calls to the strongly ordered 
is invoked within ``rcu_dynticks_eqs_enter()`` at idle-entry

time and within ``rcu_dynticks_eqs_exit()`` at idle-exit time.

The grace-period kthread invokes first ``ct_rcu_watching_cpu_acquire()``

(preceded by a full memory barrier) and ``rcu_dynticks_in_eqs_since()``

(preceded by a full memory barrier) and ``rcu_watching_snap_stopped_since()``

(both of which rely on acquire semantics) to detect idle CPUs.



+-----------------------------------------------------------------------+

kernel/rcu/tree.c

+17 −6
Original line number Diff line number Diff line
@@ -308,12 +308,20 @@ static bool rcu_watching_snap_in_eqs(int snap) 
	return !(snap & CT_RCU_WATCHING);

}



/*

 * Return true if the CPU corresponding to the specified rcu_data

 * structure has spent some time in an extended quiescent state since

 * rcu_dynticks_snap() returned the specified snapshot.

/**

 * rcu_watching_snap_stopped_since() - Has RCU stopped watching a given CPU

 * since the specified @snap?

 *

 * @rdp: The rcu_data corresponding to the CPU for which to check EQS.

 * @snap: rcu_watching snapshot taken when the CPU wasn't in an EQS.

 *

 * Returns true if the CPU corresponding to @rdp has spent some time in an

 * extended quiescent state since @snap. Note that this doesn't check if it

 * /still/ is in an EQS, just that it went through one since @snap.

 *

 * This is meant to be used in a loop waiting for a CPU to go through an EQS.

 */

static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)

static bool rcu_watching_snap_stopped_since(struct rcu_data *rdp, int snap)

{

	/*

	 * The first failing snapshot is already ordered against the accesses
@@ -323,6 +331,9 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) 
	 * performed by the remote CPU prior to entering idle and therefore can

	 * rely solely on acquire semantics.

	 */

	if (WARN_ON_ONCE(rcu_watching_snap_in_eqs(snap)))

		return true;



	return snap != ct_rcu_watching_cpu_acquire(rdp->cpu);

}
@@ -815,7 +826,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) 
	 * read-side critical section that started before the beginning

	 * of the current RCU grace period.

	 */

	if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {

	if (rcu_watching_snap_stopped_since(rdp, rdp->dynticks_snap)) {

		trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));

		rcu_gpnum_ovf(rnp, rdp);

		return 1;

kernel/rcu/tree_exp.h

+1 −1
Original line number Diff line number Diff line
@@ -400,7 +400,7 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp) 
		unsigned long mask = rdp->grpmask;



retry_ipi:

		if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {

		if (rcu_watching_snap_stopped_since(rdp, rdp->exp_dynticks_snap)) {

			mask_ofl_test |= mask;

			continue;

		}