From: Thomas Gleixner Date: Mon, 1 Feb 2021 10:01:39 +0000 (+0000) Subject: futex: Sanitize exit state handling X-Git-Tag: v4.9.255~22 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0ba263f744eec50c37d7d5bc1fd67a0ca7d81742;p=thirdparty%2Fkernel%2Fstable.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 Signed-off-by: Lee Jones Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/futex.c b/kernel/futex.c index 482000996b983..f1e8ba64fe8ae 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3311,16 +3311,19 @@ 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);