Commit-ID:  1dbb6704de91b169a58d0c8221624afd6a95cfc7
Gitweb:     http://git.kernel.org/tip/1dbb6704de91b169a58d0c8221624afd6a95cfc7
Author:     Paolo Bonzini <pbonz...@redhat.com>
AuthorDate: Tue, 1 Aug 2017 17:24:04 +0200
Committer:  Ingo Molnar <mi...@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:28:56 +0200

jump_label: 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), 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 <pbonz...@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Eric Dumazet <eric.duma...@gmail.com>
Cc: Jason Baron <jba...@akamai.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Link: 
http://lkml.kernel.org/r/1501601046-35683-2-git-send-email-pbonz...@redhat.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
 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 2afd74b..740a42e 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 d11c506..833eeca 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)
 {

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