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-rw-r--r--Documentation/static-keys.txt15
-rw-r--r--include/linux/jump_label.h11
-rw-r--r--kernel/jump_label.c22
3 files changed, 42 insertions, 6 deletions
diff --git a/Documentation/static-keys.txt b/Documentation/static-keys.txt
index 870b4be3cb11..ab16efe0c79d 100644
--- a/Documentation/static-keys.txt
+++ b/Documentation/static-keys.txt
@@ -154,6 +154,21 @@ and 'static_key_count()'. In general, if you use these functions, they
should be protected with the same mutex used around the enable/disable
or increment/decrement function.
+Note that switching branches results in some locks being taken,
+particularly the CPU hotplug lock (in order to avoid races against
+CPUs being brought in the kernel whilst the kernel is getting
+patched). Calling the static key API from within a hotplug notifier is
+thus a sure deadlock recipe. In order to still allow use of the
+functionnality, the following functions are provided:
+
+ static_key_enable_cpuslocked()
+ static_key_disable_cpuslocked()
+ static_branch_enable_cpuslocked()
+ static_branch_disable_cpuslocked()
+
+These functions are *not* general purpose, and must only be used when
+you really know that you're in the above context, and no other.
+
Where an array of keys is required, it can be defined as::
DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 740a42ea7f7f..cd5861651b17 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -163,6 +163,8 @@ extern void jump_label_apply_nops(struct module *mod);
extern int static_key_count(struct static_key *key);
extern void static_key_enable(struct static_key *key);
extern void static_key_disable(struct static_key *key);
+extern void static_key_enable_cpuslocked(struct static_key *key);
+extern void static_key_disable_cpuslocked(struct static_key *key);
/*
* We should be using ATOMIC_INIT() for initializing .enabled, but
@@ -254,6 +256,9 @@ static inline void static_key_disable(struct static_key *key)
atomic_set(&key->enabled, 0);
}
+#define static_key_enable_cpuslocked(k) static_key_enable((k))
+#define static_key_disable_cpuslocked(k) static_key_disable((k))
+
#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
@@ -415,8 +420,10 @@ extern bool ____wrong_branch_error(void);
* Normal usage; boolean enable/disable.
*/
-#define static_branch_enable(x) static_key_enable(&(x)->key)
-#define static_branch_disable(x) static_key_disable(&(x)->key)
+#define static_branch_enable(x) static_key_enable(&(x)->key)
+#define static_branch_disable(x) static_key_disable(&(x)->key)
+#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
+#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
#endif /* __ASSEMBLY__ */
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index cc6d815c75ed..0bf2e8f5244a 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -126,15 +126,15 @@ void static_key_slow_inc(struct static_key *key)
}
EXPORT_SYMBOL_GPL(static_key_slow_inc);
-void static_key_enable(struct static_key *key)
+void static_key_enable_cpuslocked(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);
@@ -145,23 +145,37 @@ void static_key_enable(struct static_key *key)
atomic_set_release(&key->enabled, 1);
}
jump_label_unlock();
+}
+EXPORT_SYMBOL_GPL(static_key_enable_cpuslocked);
+
+void static_key_enable(struct static_key *key)
+{
+ cpus_read_lock();
+ static_key_enable_cpuslocked(key);
cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(static_key_enable);
-void static_key_disable(struct static_key *key)
+void static_key_disable_cpuslocked(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();
+}
+EXPORT_SYMBOL_GPL(static_key_disable_cpuslocked);
+
+void static_key_disable(struct static_key *key)
+{
+ cpus_read_lock();
+ static_key_disable_cpuslocked(key);
cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(static_key_disable);