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Commit f9b0c6c5 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Greg Kroah-Hartman
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futex: Add mutex around futex exit 



commit 3f186d974826847a07bc7964d79ec4eded475ad9 upstream

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: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20191106224556.845798895@linutronix.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ab892020

include/linux/futex.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -68,6 +68,7 @@ static inline void futex_init_task(struct task_struct *tsk) 
	INIT_LIST_HEAD(&tsk->pi_state_list);

	INIT_LIST_HEAD(&tsk->pi_state_list);

	tsk->pi_state_cache = NULL;

	tsk->pi_state_cache = NULL;

	tsk->futex_state = FUTEX_STATE_OK;

	tsk->futex_state = FUTEX_STATE_OK;

	mutex_init(&tsk->futex_exit_mutex);

}

}





void futex_exit_recursive(struct task_struct *tsk);

void futex_exit_recursive(struct task_struct *tsk);

include/linux/sched.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -996,6 +996,7 @@ struct task_struct { 
#endif

#endif

	struct list_head		pi_state_list;

	struct list_head		pi_state_list;

	struct futex_pi_state		*pi_state_cache;

	struct futex_pi_state		*pi_state_cache;

	struct mutex			futex_exit_mutex;

	unsigned int			futex_state;

	unsigned int			futex_state;

#endif

#endif

#ifdef CONFIG_PERF_EVENTS

#ifdef CONFIG_PERF_EVENTS

kernel/futex.c

+16 −0
Original line number Original line Diff line number Diff line
@@ -3735,11 +3735,22 @@ static void futex_cleanup(struct task_struct *tsk) 
 */

 */

void futex_exit_recursive(struct task_struct *tsk)

void futex_exit_recursive(struct task_struct *tsk)

{

{

	/* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */

	if (tsk->futex_state == FUTEX_STATE_EXITING)

		mutex_unlock(&tsk->futex_exit_mutex);

	tsk->futex_state = FUTEX_STATE_DEAD;

	tsk->futex_state = FUTEX_STATE_DEAD;

}

}





static void futex_cleanup_begin(struct task_struct *tsk)

static void futex_cleanup_begin(struct task_struct *tsk)

{

{

	/*

	 * Prevent various race issues against a concurrent incoming waiter

	 * including live locks by forcing the waiter to block on

	 * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in

	 * attach_to_pi_owner().

	 */

	mutex_lock(&tsk->futex_exit_mutex);



	/*

	/*

	 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.

	 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.

	 *

	 *
@@ -3763,6 +3774,11 @@ static void futex_cleanup_end(struct task_struct *tsk, int state) 
	 * take another loop until it becomes visible.

	 * take another loop until it becomes visible.

	 */

	 */

	tsk->futex_state = state;

	tsk->futex_state = state;

	/*

	 * Drop the exit protection. This unblocks waiters which observed

	 * FUTEX_STATE_EXITING to reevaluate the state.

	 */

	mutex_unlock(&tsk->futex_exit_mutex);

}

}





void futex_exec_release(struct task_struct *tsk)

void futex_exec_release(struct task_struct *tsk)