futex: Add mutex around futex exit

The mutex will be used in subsequent changes to replace the busy looping of
a waiter when the futex owner is currently executing the exit cleanup to
prevent a potential live lock.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20191106224556.845798895@linutronix.de

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 9f2792427d64..5cc3fed27d4c 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -65,6 +65,7 @@ static inline void futex_init_task(struct task_struct *tsk)
 	INIT_LIST_HEAD(&tsk->pi_state_list);
 	tsk->pi_state_cache = NULL;
 	tsk->futex_state = FUTEX_STATE_OK;
+	mutex_init(&tsk->futex_exit_mutex);
 }
 
 void futex_exit_recursive(struct task_struct *tsk);