tree f34e198b527f5a69380b72a311076e1f26e26268
parent e1333462e3cf933ab860c693ef1ff50775c7ea7f
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1526136140 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1531435132 -0700

rcu: Don't funnel-lock above leaf node if GP in progress

The old grace-period start code would acquire only the leaf's rcu_node
structure's ->lock if that structure believed that a grace period was
in progress.  The new code advances to the leaf's parent in this case,
needlessly acquiring then leaf's parent's ->lock.  This commit therefore
checks the grace-period state after marking the leaf with the need for
the specified grace period, and if the leaf believes that a grace period
is in progress, takes an early exit.

Reported-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add "Startedleaf" tracing as suggested by Joel Fernandes. ]