Commit df2bf8f7 authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Paul E. McKenney
Browse files

rcu: Use better variable names in funnel locking loop 

The funnel locking loop in rcu_start_this_gp uses rcu_root as a
temporary variable while walking the combining tree. This causes a
tiresome exercise of a code reader reminding themselves that rcu_root
may not be root. Lets just call it rnp, and rename other variables as
well to be more appropriate.

Original patch: https://patchwork.kernel.org/patch/10396577/



Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Fix name in comment as well. ]
parent b73de91d

kernel/rcu/tree.c

+32 −32
Original line number Diff line number Diff line
@@ -1554,7 +1554,7 @@ static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, 


/*

 * rcu_start_this_gp - Request the start of a particular grace period

 * @rnp: The leaf node of the CPU from which to start.

 * @rnp_start: The leaf node of the CPU from which to start.

 * @rdp: The rcu_data corresponding to the CPU from which to start.

 * @gp_seq_req: The gp_seq of the grace period to start.

 *
@@ -1568,74 +1568,74 @@ static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, 
 *

 * Returns true if the GP thread needs to be awakened else false.

 */

static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,

static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,

			      unsigned long gp_seq_req)

{

	bool ret = false;

	struct rcu_state *rsp = rdp->rsp;

	struct rcu_node *rnp_root;

	struct rcu_node *rnp;



	/*

	 * Use funnel locking to either acquire the root rcu_node

	 * structure's lock or bail out if the need for this grace period

	 * has already been recorded -- or has already started.  If there

	 * is already a grace period in progress in a non-leaf node, no

	 * recording is needed because the end of the grace period will

	 * scan the leaf rcu_node structures.  Note that rnp->lock must

	 * not be released.

	 */

	raw_lockdep_assert_held_rcu_node(rnp);

	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startleaf"));

	for (rnp_root = rnp; 1; rnp_root = rnp_root->parent) {

		if (rnp_root != rnp)

			raw_spin_lock_rcu_node(rnp_root);

		if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_req) ||

		    rcu_seq_started(&rnp_root->gp_seq, gp_seq_req) ||

		    (rnp != rnp_root &&

		     rcu_seq_state(rcu_seq_current(&rnp_root->gp_seq)))) {

			trace_rcu_this_gp(rnp_root, rdp, gp_seq_req,

	 * has already been recorded -- or if that grace period has in

	 * fact already started.  If there is already a grace period in

	 * progress in a non-leaf node, no recording is needed because the

	 * end of the grace period will scan the leaf rcu_node structures.

	 * Note that rnp_start->lock must not be released.

	 */

	raw_lockdep_assert_held_rcu_node(rnp_start);

	trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));

	for (rnp = rnp_start; 1; rnp = rnp->parent) {

		if (rnp != rnp_start)

			raw_spin_lock_rcu_node(rnp);

		if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||

		    rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||

		    (rnp != rnp_start &&

		     rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {

			trace_rcu_this_gp(rnp, rdp, gp_seq_req,

					  TPS("Prestarted"));

			goto unlock_out;

		}

		rnp_root->gp_seq_needed = gp_seq_req;

		if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {

		rnp->gp_seq_needed = gp_seq_req;

		if (rcu_seq_state(rcu_seq_current(&rnp_start->gp_seq))) {

			/*

			 * We just marked the leaf, and a grace period

			 * is in progress, which means that rcu_gp_cleanup()

			 * will see the marking.  Bail to reduce contention.

			 */

			trace_rcu_this_gp(rnp, rdp, gp_seq_req,

			trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,

					  TPS("Startedleaf"));

			goto unlock_out;

		}

		if (rnp_root != rnp && rnp_root->parent != NULL)

			raw_spin_unlock_rcu_node(rnp_root);

		if (!rnp_root->parent)

		if (rnp != rnp_start && rnp->parent != NULL)

			raw_spin_unlock_rcu_node(rnp);

		if (!rnp->parent)

			break;  /* At root, and perhaps also leaf. */

	}



	/* If GP already in progress, just leave, otherwise start one. */

	if (rcu_gp_in_progress(rsp)) {

		trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, TPS("Startedleafroot"));

		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));

		goto unlock_out;

	}

	trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, TPS("Startedroot"));

	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));

	WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);

	rsp->gp_req_activity = jiffies;

	if (!rsp->gp_kthread) {

		trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, TPS("NoGPkthread"));

		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));

		goto unlock_out;

	}

	trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq"));

	ret = true;  /* Caller must wake GP kthread. */

unlock_out:

	/* Push furthest requested GP to leaf node and rcu_data structure. */

	if (ULONG_CMP_LT(gp_seq_req, rnp_root->gp_seq_needed)) {

		rnp->gp_seq_needed = rnp_root->gp_seq_needed;

		rdp->gp_seq_needed = rnp_root->gp_seq_needed;

	if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {

		rnp_start->gp_seq_needed = rnp->gp_seq_needed;

		rdp->gp_seq_needed = rnp->gp_seq_needed;

	}

	if (rnp != rnp_root)

		raw_spin_unlock_rcu_node(rnp_root);

	if (rnp != rnp_start)

		raw_spin_unlock_rcu_node(rnp);

	return ret;

}

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