0b28067688
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>
53 lines
1.4 KiB
C
53 lines
1.4 KiB
C
#ifndef __LINUX_SMPLOCK_H
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#define __LINUX_SMPLOCK_H
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#ifdef CONFIG_LOCK_KERNEL
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#include <linux/sched.h>
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#define kernel_locked() (current->lock_depth >= 0)
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extern int __lockfunc __reacquire_kernel_lock(void);
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extern void __lockfunc __release_kernel_lock(void);
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/*
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* Release/re-acquire global kernel lock for the scheduler
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*/
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#define release_kernel_lock(tsk) do { \
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if (unlikely((tsk)->lock_depth >= 0)) \
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__release_kernel_lock(); \
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} while (0)
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static inline int reacquire_kernel_lock(struct task_struct *task)
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{
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if (unlikely(task->lock_depth >= 0))
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return __reacquire_kernel_lock();
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return 0;
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}
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extern void __lockfunc lock_kernel(void) __acquires(kernel_lock);
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extern void __lockfunc unlock_kernel(void) __releases(kernel_lock);
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/*
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* Various legacy drivers don't really need the BKL in a specific
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* function, but they *do* need to know that the BKL became available.
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* This function just avoids wrapping a bunch of lock/unlock pairs
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* around code which doesn't really need it.
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*/
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static inline void cycle_kernel_lock(void)
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{
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lock_kernel();
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unlock_kernel();
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}
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#else
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#define lock_kernel() do { } while(0)
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#define unlock_kernel() do { } while(0)
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#define release_kernel_lock(task) do { } while(0)
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#define cycle_kernel_lock() do { } while(0)
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#define reacquire_kernel_lock(task) 0
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#define kernel_locked() 1
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#endif /* CONFIG_LOCK_KERNEL */
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#endif /* __LINUX_SMPLOCK_H */
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