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rcu: Use better variable names in funnel locking loop

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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: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Fix name in comment as well. ]
This commit is contained in:
Joel Fernandes (Google) 2018-05-22 23:38:14 -07:00 committed by Paul E. McKenney
parent b73de91d6a
commit df2bf8f7f7
1 changed files with 32 additions and 32 deletions
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64
kernel/rcu/tree.c
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@ -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 * 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. * @rdp: The rcu_data corresponding to the CPU from which to start.
* @gp_seq_req: The gp_seq of the grace period 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. * 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) unsigned long gp_seq_req)
{ {
bool ret = false; bool ret = false;
struct rcu_state *rsp = rdp->rsp; 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 * Use funnel locking to either acquire the root rcu_node
* structure's lock or bail out if the need for this grace period * structure's lock or bail out if the need for this grace period
* has already been recorded -- or has already started. If there * has already been recorded -- or if that grace period has in
* is already a grace period in progress in a non-leaf node, no * fact already started. If there is already a grace period in
* recording is needed because the end of the grace period will * progress in a non-leaf node, no recording is needed because the
* scan the leaf rcu_node structures. Note that rnp->lock must * end of the grace period will scan the leaf rcu_node structures.
* not be released. * Note that rnp_start->lock must not be released.
*/ */
raw_lockdep_assert_held_rcu_node(rnp); raw_lockdep_assert_held_rcu_node(rnp_start);
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startleaf")); trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
for (rnp_root = rnp; 1; rnp_root = rnp_root->parent) { for (rnp = rnp_start; 1; rnp = rnp->parent) {
if (rnp_root != rnp) if (rnp != rnp_start)
raw_spin_lock_rcu_node(rnp_root); raw_spin_lock_rcu_node(rnp);
if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_req) || if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
rcu_seq_started(&rnp_root->gp_seq, gp_seq_req) || rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
(rnp != rnp_root && (rnp != rnp_start &&
rcu_seq_state(rcu_seq_current(&rnp_root->gp_seq)))) { rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, trace_rcu_this_gp(rnp, rdp, gp_seq_req,
TPS("Prestarted")); TPS("Prestarted"));
goto unlock_out; goto unlock_out;
} }
rnp_root->gp_seq_needed = gp_seq_req; rnp->gp_seq_needed = gp_seq_req;
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) { if (rcu_seq_state(rcu_seq_current(&rnp_start->gp_seq))) {
/* /*
* We just marked the leaf, and a grace period * We just marked the leaf, and a grace period
* is in progress, which means that rcu_gp_cleanup() * is in progress, which means that rcu_gp_cleanup()
* will see the marking. Bail to reduce contention. * 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")); TPS("Startedleaf"));
goto unlock_out; goto unlock_out;
} }
if (rnp_root != rnp && rnp_root->parent != NULL) if (rnp != rnp_start && rnp->parent != NULL)
raw_spin_unlock_rcu_node(rnp_root); raw_spin_unlock_rcu_node(rnp);
if (!rnp_root->parent) if (!rnp->parent)
break; /* At root, and perhaps also leaf. */ break; /* At root, and perhaps also leaf. */
} }
/* If GP already in progress, just leave, otherwise start one. */ /* If GP already in progress, just leave, otherwise start one. */
if (rcu_gp_in_progress(rsp)) { 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; 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); WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
rsp->gp_req_activity = jiffies; rsp->gp_req_activity = jiffies;
if (!rsp->gp_kthread) { 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; goto unlock_out;
} }
trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq")); trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq"));
ret = true; /* Caller must wake GP kthread. */ ret = true; /* Caller must wake GP kthread. */
unlock_out: unlock_out:
/* Push furthest requested GP to leaf node and rcu_data structure. */ /* Push furthest requested GP to leaf node and rcu_data structure. */
if (ULONG_CMP_LT(gp_seq_req, rnp_root->gp_seq_needed)) { if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
rnp->gp_seq_needed = rnp_root->gp_seq_needed; rnp_start->gp_seq_needed = rnp->gp_seq_needed;
rdp->gp_seq_needed = rnp_root->gp_seq_needed; rdp->gp_seq_needed = rnp->gp_seq_needed;
} }
if (rnp != rnp_root) if (rnp != rnp_start)
raw_spin_unlock_rcu_node(rnp_root); raw_spin_unlock_rcu_node(rnp);
return ret; return ret;
} }