diff options
Diffstat (limited to 'lib/kernel_lock.c')
| -rw-r--r-- | lib/kernel_lock.c | 264 |
1 files changed, 264 insertions, 0 deletions
diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c new file mode 100644 index 00000000000..99b0ae3d51d --- /dev/null +++ b/lib/kernel_lock.c @@ -0,0 +1,264 @@ +/* + * lib/kernel_lock.c + * + * This is the traditional BKL - big kernel lock. Largely + * relegated to obsolescense, but used by various less + * important (or lazy) subsystems. + */ +#include <linux/smp_lock.h> +#include <linux/module.h> +#include <linux/kallsyms.h> + +#if defined(CONFIG_PREEMPT) && defined(__smp_processor_id) && \ + defined(CONFIG_DEBUG_PREEMPT) + +/* + * Debugging check. + */ +unsigned int smp_processor_id(void) +{ + unsigned long preempt_count = preempt_count(); + int this_cpu = __smp_processor_id(); + cpumask_t this_mask; + + if (likely(preempt_count)) + goto out; + + if (irqs_disabled()) + goto out; + + /* + * Kernel threads bound to a single CPU can safely use + * smp_processor_id(): + */ + this_mask = cpumask_of_cpu(this_cpu); + + if (cpus_equal(current->cpus_allowed, this_mask)) + goto out; + + /* + * It is valid to assume CPU-locality during early bootup: + */ + if (system_state != SYSTEM_RUNNING) + goto out; + + /* + * Avoid recursion: + */ + preempt_disable(); + + if (!printk_ratelimit()) + goto out_enable; + + printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count(), current->comm, current->pid); + print_symbol("caller is %s\n", (long)__builtin_return_address(0)); + dump_stack(); + +out_enable: + preempt_enable_no_resched(); +out: + return this_cpu; +} + +EXPORT_SYMBOL(smp_processor_id); + +#endif /* PREEMPT && __smp_processor_id && DEBUG_PREEMPT */ + +#ifdef CONFIG_PREEMPT_BKL +/* + * The 'big kernel semaphore' + * + * This mutex is taken and released recursively by lock_kernel() + * and unlock_kernel(). It is transparently dropped and reaquired + * over schedule(). It is used to protect legacy code that hasn't + * been migrated to a proper locking design yet. + * + * Note: code locked by this semaphore will only be serialized against + * other code using the same locking facility. The code guarantees that + * the task remains on the same CPU. + * + * Don't use in new code. + */ +static DECLARE_MUTEX(kernel_sem); + +/* + * Re-acquire the kernel semaphore. + * + * This function is called with preemption off. + * + * We are executing in schedule() so the code must be extremely careful + * about recursion, both due to the down() and due to the enabling of + * preemption. schedule() will re-check the preemption flag after + * reacquiring the semaphore. + */ +int __lockfunc __reacquire_kernel_lock(void) +{ + struct task_struct *task = current; + int saved_lock_depth = task->lock_depth; + + BUG_ON(saved_lock_depth < 0); + + task->lock_depth = -1; + preempt_enable_no_resched(); + + down(&kernel_sem); + + preempt_disable(); + task->lock_depth = saved_lock_depth; + + return 0; +} + +void __lockfunc __release_kernel_lock(void) +{ + up(&kernel_sem); +} + +/* + * Getting the big kernel semaphore. + */ +void __lockfunc lock_kernel(void) +{ + struct task_struct *task = current; + int depth = task->lock_depth + 1; + + if (likely(!depth)) + /* + * No recursion worries - we set up lock_depth _after_ + */ + down(&kernel_sem); + + task->lock_depth = depth; +} + +void __lockfunc unlock_kernel(void) +{ + struct task_struct *task = current; + + BUG_ON(task->lock_depth < 0); + + if (likely(--task->lock_depth < 0)) + up(&kernel_sem); +} + +#else + +/* + * The 'big kernel lock' + * + * This spinlock is taken and released recursively by lock_kernel() + * and unlock_kernel(). It is transparently dropped and reaquired + * over schedule(). It is used to protect legacy code that hasn't + * been migrated to a proper locking design yet. + * + * Don't use in new code. + */ +static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kernel_flag); + + +/* + * Acquire/release the underlying lock from the scheduler. + * + * This is called with preemption disabled, and should + * return an error value if it cannot get the lock and + * TIF_NEED_RESCHED gets set. + * + * If it successfully gets the lock, it should increment + * the preemption count like any spinlock does. + * + * (This works on UP too - _raw_spin_trylock will never + * return false in that case) + */ +int __lockfunc __reacquire_kernel_lock(void) +{ + while (!_raw_spin_trylock(&kernel_flag)) { + if (test_thread_flag(TIF_NEED_RESCHED)) + return -EAGAIN; + cpu_relax(); + } + preempt_disable(); + return 0; +} + +void __lockfunc __release_kernel_lock(void) +{ + _raw_spin_unlock(&kernel_flag); + preempt_enable_no_resched(); +} + +/* + * These are the BKL spinlocks - we try to be polite about preemption. + * If SMP is not on (ie UP preemption), this all goes away because the + * _raw_spin_trylock() will always succeed. + */ +#ifdef CONFIG_PREEMPT +static inline void __lock_kernel(void) +{ + preempt_disable(); + if (unlikely(!_raw_spin_trylock(&kernel_flag))) { + /* + * If preemption was disabled even before this + * was called, there's nothing we can be polite + * about - just spin. + */ + if (preempt_count() > 1) { + _raw_spin_lock(&kernel_flag); + return; + } + + /* + * Otherwise, let's wait for the kernel lock + * with preemption enabled.. + */ + do { + preempt_enable(); + while (spin_is_locked(&kernel_flag)) + cpu_relax(); + preempt_disable(); + } while (!_raw_spin_trylock(&kernel_flag)); + } +} + +#else + +/* + * Non-preemption case - just get the spinlock + */ +static inline void __lock_kernel(void) +{ + _raw_spin_lock(&kernel_flag); +} +#endif + +static inline void __unlock_kernel(void) +{ + _raw_spin_unlock(&kernel_flag); + preempt_enable(); +} + +/* + * Getting the big kernel lock. + * + * This cannot happen asynchronously, so we only need to + * worry about other CPU's. + */ +void __lockfunc lock_kernel(void) +{ + int depth = current->lock_depth+1; + if (likely(!depth)) + __lock_kernel(); + current->lock_depth = depth; +} + +void __lockfunc unlock_kernel(void) +{ + BUG_ON(current->lock_depth < 0); + if (likely(--current->lock_depth < 0)) + __unlock_kernel(); +} + +#endif + +EXPORT_SYMBOL(lock_kernel); +EXPORT_SYMBOL(unlock_kernel); + |