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>
diff --git a/include/linux/smp_lock.h b/include/linux/smp_lock.h
index aab3a4c..813be59 100644
--- a/include/linux/smp_lock.h
+++ b/include/linux/smp_lock.h
@@ -27,11 +27,24 @@
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