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Thomas Gleixner authored
The waitqueue which is used in struct futex_q is a leftover from the futexfd implementation. There is no need to use a waitqueue at all, as the waiting task is the only user of it. The waitqueue just adds additional locking and a loop in the wake up path which both can be avoided. We have already a task reference in struct futex_q which is used for PI futexes. Use it for normal futexes as well and just wake up the task directly. The logic of signalling the futex wakeup via setting q->lock_ptr to NULL is kept with the difference that we set it NULL before doing the wakeup. This opens an exit race window vs. a non futex wake up of the to be woken up task, which we prevent with get_task_struct / put_task_struct on the waiter. [ Impact: simplification ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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