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Date: Mon, 31 Jul 2017 15:21:59 -0400 (EDT)
From: Paolo Bonzini <pbonzini@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
tglx@...utronix.de, mingo@...nel.org, dvyukov@...gle.com,
hpa@...or.com, linux-tip-commits@...r.kernel.org,
Steven Rostedt <rostedt@...dmis.org>,
Dima Zavin <dmitriyz@...mo.com>
Subject: Re: [tip:locking/urgent] locking/static_key: Fix concurrent
static_key_slow_inc()
> > > Isn't that what we have static_key_enable() for? Which btw also uses
> > > static_key_count() outside of the mutex.
> >
> > Yes, they should be fixed and net/ can then use static_key_enable.
>
> Right, let me try and fix _enable().
Here is what I scribbled before leaving the office. (What was missing:
documentation for how to use static_key_enabled/count, testing).
>From c0bdcc89e26fb16cdc564485232bebcd1e0cc102 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@...hat.com>
Date: Mon, 31 Jul 2017 16:46:04 +0200
Subject: [PATCH 1/3] jump_labels: fix concurrent static_key_enable/disable()
static_key_enable/disable are trying to cap the static key count to
0/1. However, their use of key->enabled is outside jump_label_lock
so they do not really ensure that.
Rewrite them to do a quick check for an already enabled (respectively,
already disabled) key, and then recheck under the jump label lock. Unlike
static_key_slow_inc/dec, a failed check under the jump label lock does
not modify key->enabled.
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
include/linux/jump_label.h | 22 +++++++++--------
kernel/jump_label.c | 59 +++++++++++++++++++++++++++++-----------------
2 files changed, 49 insertions(+), 32 deletions(-)
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 2afd74b9d844..8fc5649476ca 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -234,22 +234,24 @@ static inline int jump_label_apply_nops(struct module *mod)
static inline void static_key_enable(struct static_key *key)
{
- int count = static_key_count(key);
-
- WARN_ON_ONCE(count < 0 || count > 1);
+ STATIC_KEY_CHECK_USE();
- if (!count)
- static_key_slow_inc(key);
+ if (atomic_read(&key->enabled) != 0) {
+ WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
+ return;
+ }
+ atomic_set(&key->enabled, 1);
}
static inline void static_key_disable(struct static_key *key)
{
- int count = static_key_count(key);
-
- WARN_ON_ONCE(count < 0 || count > 1);
+ STATIC_KEY_CHECK_USE();
- if (count)
- static_key_slow_dec(key);
+ if (atomic_read(&key->enabled) != 1) {
+ WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
+ return;
+ }
+ atomic_set(&key->enabled, 0);
}
#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index d11c506a6ac3..47a3e927b87e 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -79,28 +79,6 @@ int static_key_count(struct static_key *key)
}
EXPORT_SYMBOL_GPL(static_key_count);
-void static_key_enable(struct static_key *key)
-{
- int count = static_key_count(key);
-
- WARN_ON_ONCE(count < 0 || count > 1);
-
- if (!count)
- static_key_slow_inc(key);
-}
-EXPORT_SYMBOL_GPL(static_key_enable);
-
-void static_key_disable(struct static_key *key)
-{
- int count = static_key_count(key);
-
- WARN_ON_ONCE(count < 0 || count > 1);
-
- if (count)
- static_key_slow_dec(key);
-}
-EXPORT_SYMBOL_GPL(static_key_disable);
-
void static_key_slow_inc(struct static_key *key)
{
int v, v1;
@@ -139,6 +117,43 @@ void static_key_slow_inc(struct static_key *key)
}
EXPORT_SYMBOL_GPL(static_key_slow_inc);
+void static_key_enable(struct static_key *key)
+{
+ STATIC_KEY_CHECK_USE();
+ if (atomic_read(&key->enabled) != 0) {
+ WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
+ return;
+ }
+
+ cpus_read_lock();
+ jump_label_lock();
+ if (atomic_read(&key->enabled) == 0) {
+ atomic_set(&key->enabled, -1);
+ jump_label_update(key);
+ atomic_set(&key->enabled, 1);
+ }
+ jump_label_unlock();
+ cpus_read_unlock();
+}
+EXPORT_SYMBOL_GPL(static_key_enable);
+
+void static_key_disable(struct static_key *key)
+{
+ STATIC_KEY_CHECK_USE();
+ if (atomic_read(&key->enabled) != 1) {
+ WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
+ return;
+ }
+
+ cpus_read_lock();
+ jump_label_lock();
+ if (atomic_cmpxchg(&key->enabled, 1, 0))
+ jump_label_update(key);
+ jump_label_unlock();
+ cpus_read_unlock();
+}
+EXPORT_SYMBOL_GPL(static_key_disable);
+
static void __static_key_slow_dec(struct static_key *key,
unsigned long rate_limit, struct delayed_work *work)
{
--
2.13.3
>From 89d89520915bb12fd330069ca8aed32a0c216ab6 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@...hat.com>
Date: Mon, 31 Jul 2017 16:48:05 +0200
Subject: [PATCH 2/3] jump_labels: do not use unserialized static_key_enabled
Any use of key->enabled (that is static_key_enabled and static_key_count)
outside jump_label_lock should handle its own serialization. The only
two that are not doing so are the UDP encapsulation static keys. Change
them to use static_key_enable, which now correctly tests key->enabled under
the jump label lock.
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
net/ipv4/udp.c | 3 +--
net/ipv6/udp.c | 3 +--
2 files changed, 2 insertions(+), 4 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b057653ceca9..9b305776fe14 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1811,8 +1811,7 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
static struct static_key udp_encap_needed __read_mostly;
void udp_encap_enable(void)
{
- if (!static_key_enabled(&udp_encap_needed))
- static_key_slow_inc(&udp_encap_needed);
+ static_key_enable(&udp_encap_needed);
}
EXPORT_SYMBOL(udp_encap_enable);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 4a3e65626e8b..27057c41d648 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -569,8 +569,7 @@ static __inline__ void udpv6_err(struct sk_buff *skb,
static struct static_key udpv6_encap_needed __read_mostly;
void udpv6_encap_enable(void)
{
- if (!static_key_enabled(&udpv6_encap_needed))
- static_key_slow_inc(&udpv6_encap_needed);
+ static_key_enable(&udpv6_encap_needed);
}
EXPORT_SYMBOL(udpv6_encap_enable);
--
2.13.3
>From 7d8f5a373c0357663683197dfc64f20abf31a892 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@...hat.com>
Date: Mon, 31 Jul 2017 16:52:07 +0200
Subject: [PATCH 3/3] cpuset: make nr_cpusets private
Any use of key->enabled (that is static_key_enabled and static_key_count)
outside jump_label_lock should handle its own serialization. In the case
of cpusets_enabled_key, the key is always incremented/decremented under
cpuset_mutex, and hence the same rule applies to nr_cpusets. The rule
*is* respected currently, but the mutex is static so nr_cpusets should
be static too.
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
include/linux/cpuset.h | 6 ------
kernel/cgroup/cpuset.c | 7 +++++++
2 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 119a3f9604b0..cedcc910b7a7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -24,12 +24,6 @@ static inline bool cpusets_enabled(void)
return static_branch_unlikely(&cpusets_enabled_key);
}
-static inline int nr_cpusets(void)
-{
- /* jump label reference count + the top-level cpuset */
- return static_key_count(&cpusets_enabled_key.key) + 1;
-}
-
static inline void cpuset_inc(void)
{
static_branch_inc(&cpusets_enabled_key);
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ca8376e5008c..6ddca2480276 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -576,6 +576,13 @@ static void update_domain_attr_tree(struct sched_domain_attr *dattr,
rcu_read_unlock();
}
+/* Must be called with cpuset_mutex held. */
+static inline int nr_cpusets(void)
+{
+ /* jump label reference count + the top-level cpuset */
+ return static_key_count(&cpusets_enabled_key.key) + 1;
+}
+
/*
* generate_sched_domains()
*
--
2.13.3
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