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91710728d1
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:
b7d5dc2107 ("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 <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-2-bigeasy@linutronix.de
91 lines
2.2 KiB
C
91 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_LOCAL_LOCK_H
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# error "Do not include directly, include linux/local_lock.h"
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#endif
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#include <linux/percpu-defs.h>
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#include <linux/lockdep.h>
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typedef struct {
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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struct task_struct *owner;
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#endif
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} local_lock_t;
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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# define LL_DEP_MAP_INIT(lockname) \
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.dep_map = { \
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.name = #lockname, \
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.wait_type_inner = LD_WAIT_CONFIG, \
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}
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#else
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# define LL_DEP_MAP_INIT(lockname)
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#endif
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#define INIT_LOCAL_LOCK(lockname) { LL_DEP_MAP_INIT(lockname) }
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#define __local_lock_init(lock) \
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do { \
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static struct lock_class_key __key; \
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\
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debug_check_no_locks_freed((void *)lock, sizeof(*lock));\
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lockdep_init_map_wait(&(lock)->dep_map, #lock, &__key, 0, LD_WAIT_CONFIG);\
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} while (0)
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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static inline void local_lock_acquire(local_lock_t *l)
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{
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lock_map_acquire(&l->dep_map);
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DEBUG_LOCKS_WARN_ON(l->owner);
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l->owner = current;
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}
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static inline void local_lock_release(local_lock_t *l)
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{
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DEBUG_LOCKS_WARN_ON(l->owner != current);
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l->owner = NULL;
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lock_map_release(&l->dep_map);
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}
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#else /* CONFIG_DEBUG_LOCK_ALLOC */
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static inline void local_lock_acquire(local_lock_t *l) { }
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static inline void local_lock_release(local_lock_t *l) { }
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#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
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#define __local_lock(lock) \
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do { \
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preempt_disable(); \
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local_lock_acquire(this_cpu_ptr(lock)); \
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} while (0)
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#define __local_lock_irq(lock) \
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do { \
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local_irq_disable(); \
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local_lock_acquire(this_cpu_ptr(lock)); \
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} while (0)
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#define __local_lock_irqsave(lock, flags) \
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do { \
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local_irq_save(flags); \
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local_lock_acquire(this_cpu_ptr(lock)); \
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} while (0)
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#define __local_unlock(lock) \
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do { \
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local_lock_release(this_cpu_ptr(lock)); \
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preempt_enable(); \
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} while (0)
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#define __local_unlock_irq(lock) \
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do { \
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local_lock_release(this_cpu_ptr(lock)); \
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local_irq_enable(); \
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} while (0)
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#define __local_unlock_irqrestore(lock, flags) \
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do { \
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local_lock_release(this_cpu_ptr(lock)); \
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local_irq_restore(flags); \
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} while (0)
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