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Commit 0b280676 authored by Jonathan Corbet's avatar Jonathan Corbet
Browse files

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: default avatarJonathan Corbet <corbet@lwn.net>
parent 6606470d

include/linux/smp_lock.h

+13 −0
Original line number Diff line number Diff line
@@ -27,11 +27,24 @@ static inline int reacquire_kernel_lock(struct task_struct *task) 
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