Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking fix from Thomas Gleixner:
 "A single fix to address a race in the static key logic"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/static_key: Fix concurrent static_key_slow_inc()

1 files changed, 13 insertions, 3 deletions

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 0536524bb9eb..68904469fba1 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -117,13 +117,18 @@ struct module;
 
 #include <linux/atomic.h>
 
+#ifdef HAVE_JUMP_LABEL
+
 static inline int static_key_count(struct static_key *key)
 {
-        return atomic_read(&key->enabled);
+        /*
+         * -1 means the first static_key_slow_inc() is in progress.
+         *  static_key_enabled() must return true, so return 1 here.
+         */
+        int n = atomic_read(&key->enabled);
+        return n >= 0 ? n : 1;
 }
 
-#ifdef HAVE_JUMP_LABEL
-
 #define JUMP_TYPE_FALSE 0UL
 #define JUMP_TYPE_TRUE  1UL
 #define JUMP_TYPE_MASK  1UL
@@ -162,6 +167,11 @@ extern void jump_label_apply_nops(struct module *mod);
 
 #else  /* !HAVE_JUMP_LABEL */
 
+static inline int static_key_count(struct static_key *key)
+{
+        return atomic_read(&key->enabled);
+}
+
 static __always_inline void jump_label_init(void)
 {
         static_key_initialized = true;