| From foo@baz Mon Feb 1 04:21:37 PM CET 2021 |
| From: Lee Jones <lee.jones@linaro.org> |
| Date: Mon, 1 Feb 2021 15:12:10 +0000 |
| Subject: futex: Sanitize exit state handling |
| To: stable@vger.kernel.org |
| Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Lee Jones <lee.jones@linaro.org> |
| Message-ID: <20210201151214.2193508-9-lee.jones@linaro.org> |
| |
| From: Thomas Gleixner <tglx@linutronix.de> |
| |
| 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 <tglx@linutronix.de> |
| Reviewed-by: Ingo Molnar <mingo@kernel.org> |
| Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Link: https://lkml.kernel.org/r/20191106224556.645603214@linutronix.de |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Signed-off-by: Lee Jones <lee.jones@linaro.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| kernel/futex.c | 17 ++++++++++------- |
| 1 file changed, 10 insertions(+), 7 deletions(-) |
| |
| --- a/kernel/futex.c |
| +++ b/kernel/futex.c |
| @@ -3276,16 +3276,19 @@ void futex_exit_recursive(struct task_st |
| |
| 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); |