One necessary step towards consolidating the three flavors of RCU is to
make sure that the resulting consolidated "one flavor to rule them all"
correctly handles networking denial-of-service attacks. One thing that
allows RCU-bh to do so is that __do_softirq() invokes rcu_bh_qs() every
so often, and so something similar has to happen for consolidated RCU.
This must be done carefully. For example, if a preemption-disabled
region of code takes an interrupt which does softirq processing before
returning, consolidated RCU must ignore the resulting rcu_bh_qs()
invocations -- preemption is still disabled, and that means an RCU
reader for the consolidated flavor.
This commit therefore creates a new rcu_softirq_qs() that is called only
from the ksoftirqd task, thus avoiding the interrupted-a-preempted-region
problem. This new rcu_softirq_qs() function invokes rcu_sched_qs(),
rcu_preempt_qs(), and rcu_preempt_deferred_qs(). The latter call handles
any deferred quiescent states.
Note that __do_softirq() still invokes rcu_bh_qs(). It will continue to
do so until a later stage of cleanup when the RCU-bh flavor is removed.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
[ paulmck: Fix !SMP issue located by kbuild test robot. ]
---
include/linux/rcutiny.h | 5 +++++
include/linux/rcutree.h | 1 +
kernel/rcu/tree.c | 7 +++++++
kernel/rcu/tree.h | 1 +
kernel/rcu/tree_plugin.h | 5 +++++
kernel/softirq.c | 2 ++
6 files changed, 21 insertions(+)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index f617ab19bb51..bcfbc40a7239 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -90,6 +90,11 @@ static inline void kfree_call_rcu(struct rcu_head *head,
call_rcu(head, func);
}
+static inline void rcu_softirq_qs(void)
+{
+ rcu_sched_qs();
+}
+
#define rcu_note_context_switch(preempt) \
do { \
rcu_sched_qs(); \
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 914655848ef6..664b580695d6 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -30,6 +30,7 @@
#ifndef __LINUX_RCUTREE_H
#define __LINUX_RCUTREE_H
+void rcu_softirq_qs(void);
void rcu_note_context_switch(bool preempt);
int rcu_needs_cpu(u64 basem, u64 *nextevt);
void rcu_cpu_stall_reset(void);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d2b6ade692c9..9b6bd12133c4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -255,6 +255,13 @@ void rcu_bh_qs(void)
}
}
+void rcu_softirq_qs(void)
+{
+ rcu_sched_qs();
+ rcu_preempt_qs();
+ rcu_preempt_deferred_qs(current);
+}
+
/*
* Steal a bit from the bottom of ->dynticks for idle entry/exit
* control. Initially this is for TLB flushing.
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 025bd2e5592b..e02c882861eb 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -433,6 +433,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
+static void rcu_preempt_qs(void);
static void rcu_preempt_note_context_switch(bool preempt);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 527a52792dce..c686bf63bba5 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -974,6 +974,11 @@ static void __init rcu_bootup_announce(void)
rcu_bootup_announce_oddness();
}
+/* Because preemptible RCU does not exist, we can ignore its QSes. */
+static void rcu_preempt_qs(void)
+{
+}
+
/*
* Because preemptible RCU does not exist, we never have to check for
* CPUs being in quiescent states.
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 6f584861d329..ebd69694144a 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -302,6 +302,8 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
}
rcu_bh_qs();
+ if (__this_cpu_read(ksoftirqd) == current)
+ rcu_softirq_qs();
local_irq_disable();
pending = local_softirq_pending();
--
2.17.1
