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Subject[PATCH 1/3] jump_labels: fix concurrent static_key_enable/disable()
Date
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), 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.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.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..740a42ea7f7f 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 6c9cb208ac48..04a574fd5844 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -78,28 +78,6 @@ 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;
@@ -136,6 +114,43 @@ 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)
{
--
1.8.3.1

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