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 rcu_node, and then finally when rcu_node is the rcu_root, lets assign it at that time.
Just a clean up patch, no logical change. Signed-off-by: Joel Fernandes (Google) <[email protected]> --- kernel/rcu/tree.c | 34 ++++++++++++++++++---------------- 1 file changed, 18 insertions(+), 16 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 9f5679ba413b..40670047d22c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1568,7 +1568,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, { bool ret = false; struct rcu_state *rsp = rdp->rsp; - struct rcu_node *rnp_root; + struct rcu_node *rnp_node, *rnp_root = NULL; /* * Use funnel locking to either acquire the root rcu_node @@ -1581,24 +1581,26 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, */ raw_lockdep_assert_held_rcu_node(rnp); trace_rcu_this_gp(rnp, rdp, gp_seq_start, 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_start) || - rcu_seq_done(&rnp_root->gp_seq, gp_seq_start) || - (rnp != rnp_root && - rcu_seq_state(rcu_seq_current(&rnp_root->gp_seq)))) { - trace_rcu_this_gp(rnp_root, rdp, gp_seq_start, + for (rnp_node = rnp; 1; rnp_node = rnp_node->parent) { + if (rnp_node != rnp) + raw_spin_lock_rcu_node(rnp_node); + if (ULONG_CMP_GE(rnp_node->gp_seq_needed, gp_seq_start) || + rcu_seq_done(&rnp_node->gp_seq, gp_seq_start) || + (rnp != rnp_node && + rcu_seq_state(rcu_seq_current(&rnp_node->gp_seq)))) { + trace_rcu_this_gp(rnp_node, rdp, gp_seq_start, TPS("Prestarted")); goto unlock_out; } - rnp_root->gp_seq_needed = gp_seq_start; + rnp_node->gp_seq_needed = gp_seq_start; if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) goto unlock_out; - if (rnp_root != rnp && rnp_root->parent != NULL) - raw_spin_unlock_rcu_node(rnp_root); - if (!rnp_root->parent) + if (rnp_node != rnp && rnp_node->parent != NULL) + raw_spin_unlock_rcu_node(rnp_node); + if (!rnp_node->parent) { + rnp_root = rnp_node; break; /* At root, and perhaps also leaf. */ + } } /* If GP already in progress, just leave, otherwise start one. */ @@ -1616,10 +1618,10 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq")); ret = true; /* Caller must wake GP kthread. */ unlock_out: - if (rnp != rnp_root) - raw_spin_unlock_rcu_node(rnp_root); + if (rnp != rnp_node) + raw_spin_unlock_rcu_node(rnp_node); /* Push furthest requested GP to leaf node and rcu_data structure. */ - if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_start)) { + if (ULONG_CMP_GE(rnp_node->gp_seq_needed, gp_seq_start)) { rnp->gp_seq_needed = gp_seq_start; rdp->gp_seq_needed = gp_seq_start; } -- 2.17.0.441.gb46fe60e1d-goog
