From: Thomas Gleixner Date: Wed, 6 Nov 2019 21:55:42 +0000 (+0100) Subject: futex: Sanitize exit state handling X-Git-Tag: v4.19.172~18 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=b45696340f5321cd7bd4f4865bae86c229d2bcc1;p=users%2Fdwmw2%2Flinux.git 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: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20191106224556.645603214@linutronix.de Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/futex.c b/kernel/futex.c index f995270a238a9..6f4b9bd7ac15f 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -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);