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Commit b4569634 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Greg Kroah-Hartman
Browse files

futex: Sanitize exit state handling 



commit 4a8e991b91aca9e20705d434677ac013974e0e30 upstream

Instead of having a smp_mb() and an empty lock/unlock of task::pi_lock move
the state setting into to the lock section.

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/20191106224556.645603214@linutronix.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 226eed1e

kernel/futex.c

+10 −7
Original line number Diff line number Diff line
@@ -3740,16 +3740,19 @@ void futex_exit_recursive(struct task_struct *tsk) 


void futex_exit_release(struct task_struct *tsk)

{

	tsk->futex_state = FUTEX_STATE_EXITING;

	/*

	 * Ensure that all new tsk->pi_lock acquisitions must observe

	 * FUTEX_STATE_EXITING. Serializes against attach_to_pi_owner().

	 */

	smp_mb();

	/*

	 * Ensure that we must observe the pi_state in exit_pi_state_list().

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

	 *

	 * This ensures that all subsequent checks of tsk->futex_state in

	 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with

	 * tsk->pi_lock held.

	 *

	 * It guarantees also that a pi_state which was queued right before

	 * the state change under tsk->pi_lock by a concurrent waiter must

	 * be observed in exit_pi_state_list().

	 */

	raw_spin_lock_irq(&tsk->pi_lock);

	tsk->futex_state = FUTEX_STATE_EXITING;

	raw_spin_unlock_irq(&tsk->pi_lock);



	futex_exec_release(tsk);