locking: Introduce local_lock()
preempt_disable() and local_irq_disable/save() are in principle per CPU big
kernel locks. This has several downsides:
- The protection scope is unknown
- Violation of protection rules is hard to detect by instrumentation
- For PREEMPT_RT such sections, unless in low level critical code, can
violate the preemptability constraints.
To address this PREEMPT_RT introduced the concept of local_locks which are
strictly per CPU.
The lock operations map to preempt_disable(), local_irq_disable/save() and
the enabling counterparts on non RT enabled kernels.
If lockdep is enabled local locks gain a lock map which tracks the usage
context. This will catch cases where an area is protected by
preempt_disable() but the access also happens from interrupt context. local
locks have identified quite a few such issues over the years, the most
recent example is:
b7d5dc21072cd ("random: add a spinlock_t to struct batched_entropy")
Aside of the lockdep coverage this also improves code readability as it
precisely annotates the protection scope.
PREEMPT_RT substitutes these local locks with 'sleeping' spinlocks to
protect such sections while maintaining preemtability and CPU locality.
local locks can replace:
- preempt_enable()/disable() pairs
- local_irq_disable/enable() pairs
- local_irq_save/restore() pairs
They are also used to replace code which implicitly disables preemption
like:
- get_cpu()/put_cpu()
- get_cpu_var()/put_cpu_var()
with PREEMPT_RT friendly constructs.
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
new file mode 100644
index 0000000..4a8795b
--- /dev/null
+++ b/include/linux/local_lock_internal.h
@@ -0,0 +1,90 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_LOCAL_LOCK_H
+# error "Do not include directly, include linux/local_lock.h"
+#endif
+
+#include <linux/percpu-defs.h>
+#include <linux/lockdep.h>
+
+typedef struct {
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ struct lockdep_map dep_map;
+ struct task_struct *owner;
+#endif
+} local_lock_t;
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+# define LL_DEP_MAP_INIT(lockname) \
+ .dep_map = { \
+ .name = #lockname, \
+ .wait_type_inner = LD_WAIT_CONFIG, \
+ }
+#else
+# define LL_DEP_MAP_INIT(lockname)
+#endif
+
+#define INIT_LOCAL_LOCK(lockname) { LL_DEP_MAP_INIT(lockname) }
+
+#define __local_lock_init(lock) \
+do { \
+ static struct lock_class_key __key; \
+ \
+ debug_check_no_locks_freed((void *)lock, sizeof(*lock));\
+ lockdep_init_map_wait(&(lock)->dep_map, #lock, &__key, 0, LD_WAIT_CONFIG);\
+} while (0)
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+static inline void local_lock_acquire(local_lock_t *l)
+{
+ lock_map_acquire(&l->dep_map);
+ DEBUG_LOCKS_WARN_ON(l->owner);
+ l->owner = current;
+}
+
+static inline void local_lock_release(local_lock_t *l)
+{
+ DEBUG_LOCKS_WARN_ON(l->owner != current);
+ l->owner = NULL;
+ lock_map_release(&l->dep_map);
+}
+
+#else /* CONFIG_DEBUG_LOCK_ALLOC */
+static inline void local_lock_acquire(local_lock_t *l) { }
+static inline void local_lock_release(local_lock_t *l) { }
+#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
+
+#define __local_lock(lock) \
+ do { \
+ preempt_disable(); \
+ local_lock_acquire(this_cpu_ptr(lock)); \
+ } while (0)
+
+#define __local_lock_irq(lock) \
+ do { \
+ local_irq_disable(); \
+ local_lock_acquire(this_cpu_ptr(lock)); \
+ } while (0)
+
+#define __local_lock_irqsave(lock, flags) \
+ do { \
+ local_irq_save(flags); \
+ local_lock_acquire(this_cpu_ptr(lock)); \
+ } while (0)
+
+#define __local_unlock(lock) \
+ do { \
+ local_lock_release(this_cpu_ptr(lock)); \
+ preempt_enable(); \
+ } while (0)
+
+#define __local_unlock_irq(lock) \
+ do { \
+ local_lock_release(this_cpu_ptr(lock)); \
+ local_irq_enable(); \
+ } while (0)
+
+#define __local_unlock_irqrestore(lock, flags) \
+ do { \
+ local_lock_release(this_cpu_ptr(lock)); \
+ local_irq_restore(flags); \
+ } while (0)
