From: Alexei Starovoitov <ast@xxxxxxxxxx> Similar to local_lock_irqsave() introduce local_trylock_irqsave(). This is inspired by 'struct local_tryirq_lock' in: https://lore.kernel.org/all/20241112-slub-percpu-caches-v1-5-ddc0bdc27e05@xxxxxxx/ Use spin_trylock in PREEMPT_RT when not in hard IRQ and not in NMI and fail instantly otherwise, since spin_trylock is not safe from IRQ due to PI issues. In !PREEMPT_RT use simple active flag to prevent IRQs or NMIs reentering locked region. Note there is no need to use local_inc for active flag. If IRQ handler grabs the same local_lock after READ_ONCE(lock->active) already completed it has to unlock it before returning. Similar with NMI handler. So there is a strict nesting of scopes. It's a per cpu lock. Multiple cpus do not access it in parallel. Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> --- include/linux/local_lock.h | 9 ++++ include/linux/local_lock_internal.h | 76 ++++++++++++++++++++++++++--- 2 files changed, 78 insertions(+), 7 deletions(-) diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h index 091dc0b6bdfb..84ee560c4f51 100644 --- a/include/linux/local_lock.h +++ b/include/linux/local_lock.h @@ -30,6 +30,15 @@ #define local_lock_irqsave(lock, flags) \ __local_lock_irqsave(lock, flags) +/** + * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable + * interrupts. Always fails in RT when in_hardirq or NMI. + * @lock: The lock variable + * @flags: Storage for interrupt flags + */ +#define local_trylock_irqsave(lock, flags) \ + __local_trylock_irqsave(lock, flags) + /** * local_unlock - Release a per CPU local lock * @lock: The lock variable diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h index 8dd71fbbb6d2..93672127c73d 100644 --- a/include/linux/local_lock_internal.h +++ b/include/linux/local_lock_internal.h @@ -9,6 +9,7 @@ #ifndef CONFIG_PREEMPT_RT typedef struct { + int active; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; struct task_struct *owner; @@ -22,7 +23,7 @@ typedef struct { .wait_type_inner = LD_WAIT_CONFIG, \ .lock_type = LD_LOCK_PERCPU, \ }, \ - .owner = NULL, + .owner = NULL, .active = 0 static inline void local_lock_acquire(local_lock_t *l) { @@ -31,6 +32,13 @@ static inline void local_lock_acquire(local_lock_t *l) l->owner = current; } +static inline void local_trylock_acquire(local_lock_t *l) +{ + lock_map_acquire_try(&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); @@ -45,6 +53,7 @@ static inline void local_lock_debug_init(local_lock_t *l) #else /* CONFIG_DEBUG_LOCK_ALLOC */ # define LOCAL_LOCK_DEBUG_INIT(lockname) static inline void local_lock_acquire(local_lock_t *l) { } +static inline void local_trylock_acquire(local_lock_t *l) { } static inline void local_lock_release(local_lock_t *l) { } static inline void local_lock_debug_init(local_lock_t *l) { } #endif /* !CONFIG_DEBUG_LOCK_ALLOC */ @@ -60,6 +69,7 @@ do { \ 0, LD_WAIT_CONFIG, LD_WAIT_INV, \ LD_LOCK_PERCPU); \ local_lock_debug_init(lock); \ + (lock)->active = 0; \ } while (0) #define __spinlock_nested_bh_init(lock) \ @@ -75,37 +85,73 @@ do { \ #define __local_lock(lock) \ do { \ + local_lock_t *l; \ preempt_disable(); \ - local_lock_acquire(this_cpu_ptr(lock)); \ + l = this_cpu_ptr(lock); \ + lockdep_assert(l->active == 0); \ + WRITE_ONCE(l->active, 1); \ + local_lock_acquire(l); \ } while (0) #define __local_lock_irq(lock) \ do { \ + local_lock_t *l; \ local_irq_disable(); \ - local_lock_acquire(this_cpu_ptr(lock)); \ + l = this_cpu_ptr(lock); \ + lockdep_assert(l->active == 0); \ + WRITE_ONCE(l->active, 1); \ + local_lock_acquire(l); \ } while (0) #define __local_lock_irqsave(lock, flags) \ do { \ + local_lock_t *l; \ local_irq_save(flags); \ - local_lock_acquire(this_cpu_ptr(lock)); \ + l = this_cpu_ptr(lock); \ + lockdep_assert(l->active == 0); \ + WRITE_ONCE(l->active, 1); \ + local_lock_acquire(l); \ } while (0) +#define __local_trylock_irqsave(lock, flags) \ + ({ \ + local_lock_t *l; \ + local_irq_save(flags); \ + l = this_cpu_ptr(lock); \ + if (READ_ONCE(l->active) == 1) { \ + local_irq_restore(flags); \ + l = NULL; \ + } else { \ + WRITE_ONCE(l->active, 1); \ + local_trylock_acquire(l); \ + } \ + !!l; \ + }) + #define __local_unlock(lock) \ do { \ - local_lock_release(this_cpu_ptr(lock)); \ + local_lock_t *l = this_cpu_ptr(lock); \ + lockdep_assert(l->active == 1); \ + WRITE_ONCE(l->active, 0); \ + local_lock_release(l); \ preempt_enable(); \ } while (0) #define __local_unlock_irq(lock) \ do { \ - local_lock_release(this_cpu_ptr(lock)); \ + local_lock_t *l = this_cpu_ptr(lock); \ + lockdep_assert(l->active == 1); \ + WRITE_ONCE(l->active, 0); \ + local_lock_release(l); \ local_irq_enable(); \ } while (0) #define __local_unlock_irqrestore(lock, flags) \ do { \ - local_lock_release(this_cpu_ptr(lock)); \ + local_lock_t *l = this_cpu_ptr(lock); \ + lockdep_assert(l->active == 1); \ + WRITE_ONCE(l->active, 0); \ + local_lock_release(l); \ local_irq_restore(flags); \ } while (0) @@ -148,6 +194,22 @@ typedef spinlock_t local_lock_t; __local_lock(lock); \ } while (0) +#define __local_trylock_irqsave(lock, flags) \ + ({ \ + __label__ out; \ + int ret = 0; \ + typecheck(unsigned long, flags); \ + flags = 0; \ + if (in_nmi() || in_hardirq()) \ + goto out; \ + migrate_disable(); \ + ret = spin_trylock(this_cpu_ptr((lock))); \ + if (!ret) \ + migrate_enable(); \ + out: \ + ret; \ + }) + #define __local_unlock(__lock) \ do { \ spin_unlock(this_cpu_ptr((__lock))); \ -- 2.43.5
