android_kernel_motorola_sm6225/include/linux/smp_lock.h
Jonathan Corbet 0b28067688 Add cycle_kernel_lock()
A number of driver functions are so obviously trivial that they do not need
the big kernel lock - at least not overtly.  It turns out that the
acquisition of the BKL in driver open() functions can perform a sort of
poor-hacker's serialization function, delaying the open operation until the
driver is certain to have completed its initialization.  Add a simple
cycle_kernel_lock() function for these cases to make it clear that there is
no need to *hold* the BKL, just to be sure that we can acquire it.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2008-06-20 14:05:53 -06:00

52 lines
1.4 KiB
C

#ifndef __LINUX_SMPLOCK_H
#define __LINUX_SMPLOCK_H
#ifdef CONFIG_LOCK_KERNEL
#include <linux/sched.h>
#define kernel_locked() (current->lock_depth >= 0)
extern int __lockfunc __reacquire_kernel_lock(void);
extern void __lockfunc __release_kernel_lock(void);
/*
* Release/re-acquire global kernel lock for the scheduler
*/
#define release_kernel_lock(tsk) do { \
if (unlikely((tsk)->lock_depth >= 0)) \
__release_kernel_lock(); \
} while (0)
static inline int reacquire_kernel_lock(struct task_struct *task)
{
if (unlikely(task->lock_depth >= 0))
return __reacquire_kernel_lock();
return 0;
}
extern void __lockfunc lock_kernel(void) __acquires(kernel_lock);
extern void __lockfunc unlock_kernel(void) __releases(kernel_lock);
/*
* Various legacy drivers don't really need the BKL in a specific
* function, but they *do* need to know that the BKL became available.
* This function just avoids wrapping a bunch of lock/unlock pairs
* around code which doesn't really need it.
*/
static inline void cycle_kernel_lock(void)
{
lock_kernel();
unlock_kernel();
}
#else
#define lock_kernel() do { } while(0)
#define unlock_kernel() do { } while(0)
#define release_kernel_lock(task) do { } while(0)
#define cycle_kernel_lock() do { } while(0)
#define reacquire_kernel_lock(task) 0
#define kernel_locked() 1
#endif /* CONFIG_LOCK_KERNEL */
#endif /* __LINUX_SMPLOCK_H */