Merge branches 'doc.2020.02.27a', 'fixes.2020.03.21a', 'kfree_rcu.2020.02.20a', ...

doc.2020.02.27a: Documentation updates.
fixes.2020.03.21a: Miscellaneous fixes.
kfree_rcu.2020.02.20a: Updates to kfree_rcu().
locktorture.2020.02.20a: Lock torture-test updates.
ovld.2020.02.20a: Updates to callback-overload handling.
rcu-tasks.2020.02.20a: RCU-tasks updates.
srcu.2020.02.20a: SRCU updates.
torture.2020.02.20a: Torture-test updates.

diff --cc Documentation/admin-guide/kernel-parameters.txt
Simple merge

diff --cc include/trace/events/rcu.h
Simple merge

diff --cc kernel/rcu/rcu.h
Simple merge

diff --cc kernel/rcu/srcutree.c
Simple merge

diff --cc kernel/rcu/tree.c
index d91c915,35292c8,909f97e,d91c915,0a9de9f,d91c915,d91c915,d91c915..550193a
--- 1/kernel/rcu/tree.c
--- 2/kernel/rcu/tree.c
--- 3/kernel/rcu/tree.c
--- 4/kernel/rcu/tree.c
--- 5/kernel/rcu/tree.c
--- 6/kernel/rcu/tree.c
--- 7/kernel/rcu/tree.c
--- 8/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@@@@@@@@ -2579,11 -2579,11 -2579,11 -2579,11 -2601,48 -2579,11 -2579,11 -2579,11 +2601,48 @@@@@@@@@ static void rcu_leak_callback(struct rc
        }
        
        /*
---- --- * Helper function for call_rcu() and friends.  The cpu argument will
---- --- * normally be -1, indicating "currently running CPU".  It may specify
---- --- * a CPU only if that CPU is a no-CBs CPU.  Currently, only rcu_barrier()
---- --- * is expected to specify a CPU.
++++ +++ * Check and if necessary update the leaf rcu_node structure's
++++ +++ * ->cbovldmask bit corresponding to the current CPU based on that CPU's
++++ +++ * number of queued RCU callbacks.  The caller must hold the leaf rcu_node
++++ +++ * structure's ->lock.
 +       */
++++ +++static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
++++ +++{
++++ +++        raw_lockdep_assert_held_rcu_node(rnp);
++++ +++        if (qovld_calc <= 0)
++++ +++                return; // Early boot and wildcard value set.
++++ +++        if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
++++ +++                WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
++++ +++        else
++++ +++                WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
++++ +++}
++++ +++
++++ +++/*
++++ +++ * Check and if necessary update the leaf rcu_node structure's
++++ +++ * ->cbovldmask bit corresponding to the current CPU based on that CPU's
++++ +++ * number of queued RCU callbacks.  No locks need be held, but the
++++ +++ * caller must have disabled interrupts.
++++ +++ *
++++ +++ * Note that this function ignores the possibility that there are a lot
++++ +++ * of callbacks all of which have already seen the end of their respective
++++ +++ * grace periods.  This omission is due to the need for no-CBs CPUs to
++++ +++ * be holding ->nocb_lock to do this check, which is too heavy for a
++++ +++ * common-case operation.
+ ++ +++ */
++++ +++static void check_cb_ovld(struct rcu_data *rdp)
++++ +++{
++++ +++        struct rcu_node *const rnp = rdp->mynode;
++++ +++
++++ +++        if (qovld_calc <= 0 ||
++++ +++            ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
++++ +++             !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
++++ +++                return; // Early boot wildcard value or already set correctly.
++++ +++        raw_spin_lock_rcu_node(rnp);
++++ +++        check_cb_ovld_locked(rdp, rnp);
++++ +++        raw_spin_unlock_rcu_node(rnp);
++++ +++}
++++ +++
++++ +++/* Helper function for call_rcu() and friends.  */
        static void
        __call_rcu(struct rcu_head *head, rcu_callback_t func)
        {

diff --cc kernel/rcu/tree_exp.h
Simple merge

diff --cc kernel/rcu/tree_plugin.h
Simple merge

diff --cc kernel/rcu/tree_stall.h
Simple merge

diff --cc kernel/rcu/update.c
Simple merge