On Sun, Mar 14, 2021 at 10:02:23PM -0700, Davidlohr Bueso wrote:
> The pi_mutex->wait_lock is irq safe and needs to enable local
> interrupts upon unlocking, matching it's corresponding
> raw_spin_lock_irq().
>
> Fixes: c74aef2d06a9f (futex: Fix pi_state->owner serialization)
> Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
> ---
> kernel/futex.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 475055715371..ded7af2ba87f 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -885,7 +885,7 @@ static void exit_pi_state_list(struct task_struct *curr)
> */
> if (head->next != next) {
> /* retain curr->pi_lock for the loop invariant */
> - raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
> + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
> spin_unlock(&hb->lock);
> put_pi_state(pi_state);
> continue;
This seems broken, afaict we own:
&hb->lock
&pi_state->pi_mutex.wait_lock
&curr->pi_lock
And we're only releasing:
&hb->lock
&pi_state->pi_mutex.wait_lock
Which leaves us holding:
&curr->pi_lock
which is also an IRQ safe lock, so enabling IRQs would be BAD.
Or am I reading this wrong?
