diff options
| -rw-r--r-- | Documentation/static-keys.txt | 15 | ||||
| -rw-r--r-- | include/linux/jump_label.h | 11 | ||||
| -rw-r--r-- | kernel/jump_label.c | 22 |
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); |