diff options
| -rw-r--r-- | include/linux/printk.h | 41 | ||||
| -rw-r--r-- | kernel/printk/printk.c | 69 | ||||
| -rw-r--r-- | lib/dump_stack.c | 38 |
3 files changed, 112 insertions, 36 deletions
diff --git a/include/linux/printk.h b/include/linux/printk.h index fe7eb2351610..1790a5521fd9 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -282,6 +282,47 @@ static inline void printk_safe_flush_on_panic(void) } #endif +#ifdef CONFIG_SMP +extern int __printk_cpu_trylock(void); +extern void __printk_wait_on_cpu_lock(void); +extern void __printk_cpu_unlock(void); + +/** + * printk_cpu_lock_irqsave() - Acquire the printk cpu-reentrant spinning + * lock and disable interrupts. + * @flags: Stack-allocated storage for saving local interrupt state, + * to be passed to printk_cpu_unlock_irqrestore(). + * + * If the lock is owned by another CPU, spin until it becomes available. + * Interrupts are restored while spinning. + */ +#define printk_cpu_lock_irqsave(flags) \ + for (;;) { \ + local_irq_save(flags); \ + if (__printk_cpu_trylock()) \ + break; \ + local_irq_restore(flags); \ + __printk_wait_on_cpu_lock(); \ + } + +/** + * printk_cpu_unlock_irqrestore() - Release the printk cpu-reentrant spinning + * lock and restore interrupts. + * @flags: Caller's saved interrupt state, from printk_cpu_lock_irqsave(). + */ +#define printk_cpu_unlock_irqrestore(flags) \ + do { \ + __printk_cpu_unlock(); \ + local_irq_restore(flags); \ + } while (0) \ + +#else + +#define printk_cpu_lock_irqsave(flags) ((void)flags) +#define printk_cpu_unlock_irqrestore(flags) ((void)flags) + +#endif /* CONFIG_SMP */ + extern int kptr_restrict; /** diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 421c35571797..9dfad0efb67f 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3531,3 +3531,72 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter) EXPORT_SYMBOL_GPL(kmsg_dump_rewind); #endif + +#ifdef CONFIG_SMP +static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1); +static atomic_t printk_cpulock_nested = ATOMIC_INIT(0); + +/** + * __printk_wait_on_cpu_lock() - Busy wait until the printk cpu-reentrant + * spinning lock is not owned by any CPU. + * + * Context: Any context. + */ +void __printk_wait_on_cpu_lock(void) +{ + do { + cpu_relax(); + } while (atomic_read(&printk_cpulock_owner) != -1); +} +EXPORT_SYMBOL(__printk_wait_on_cpu_lock); + +/** + * __printk_cpu_trylock() - Try to acquire the printk cpu-reentrant + * spinning lock. + * + * If no processor has the lock, the calling processor takes the lock and + * becomes the owner. If the calling processor is already the owner of the + * lock, this function succeeds immediately. + * + * Context: Any context. Expects interrupts to be disabled. + * Return: 1 on success, otherwise 0. + */ +int __printk_cpu_trylock(void) +{ + int cpu; + int old; + + cpu = smp_processor_id(); + + old = atomic_cmpxchg(&printk_cpulock_owner, -1, cpu); + if (old == -1) { + /* This CPU is now the owner. */ + return 1; + } else if (old == cpu) { + /* This CPU is already the owner. */ + atomic_inc(&printk_cpulock_nested); + return 1; + } + + return 0; +} +EXPORT_SYMBOL(__printk_cpu_trylock); + +/** + * __printk_cpu_unlock() - Release the printk cpu-reentrant spinning lock. + * + * The calling processor must be the owner of the lock. + * + * Context: Any context. Expects interrupts to be disabled. + */ +void __printk_cpu_unlock(void) +{ + if (atomic_read(&printk_cpulock_nested)) { + atomic_dec(&printk_cpulock_nested); + return; + } + + atomic_set(&printk_cpulock_owner, -1); +} +EXPORT_SYMBOL(__printk_cpu_unlock); +#endif /* CONFIG_SMP */ diff --git a/lib/dump_stack.c b/lib/dump_stack.c index f5a33b6f773f..5ebf4375fa8c 100644 --- a/lib/dump_stack.c +++ b/lib/dump_stack.c @@ -84,50 +84,16 @@ static void __dump_stack(void) * * Architectures can override this implementation by implementing its own. */ -#ifdef CONFIG_SMP -static atomic_t dump_lock = ATOMIC_INIT(-1); - asmlinkage __visible void dump_stack(void) { unsigned long flags; - int was_locked; - int old; - int cpu; /* * Permit this cpu to perform nested stack dumps while serialising * against other CPUs */ -retry: - local_irq_save(flags); - cpu = smp_processor_id(); - old = atomic_cmpxchg(&dump_lock, -1, cpu); - if (old == -1) { - was_locked = 0; - } else if (old == cpu) { - was_locked = 1; - } else { - local_irq_restore(flags); - /* - * Wait for the lock to release before jumping to - * atomic_cmpxchg() in order to mitigate the thundering herd - * problem. - */ - do { cpu_relax(); } while (atomic_read(&dump_lock) != -1); - goto retry; - } - - __dump_stack(); - - if (!was_locked) - atomic_set(&dump_lock, -1); - - local_irq_restore(flags); -} -#else -asmlinkage __visible void dump_stack(void) -{ + printk_cpu_lock_irqsave(flags); __dump_stack(); + printk_cpu_unlock_irqrestore(flags); } -#endif EXPORT_SYMBOL(dump_stack); |