Add cycle_kernel_lock() (0b280676) · Commits · 戴 / test

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>

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

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