On Fri, 2009-08-07 at 15:20 -0700, Darren Hart wrote:
> From: Darren Hart <dvhltc@xxxxxxxxxx>
>
> If futex_requeue(requeue_pi=1) finds a futex_q that was created by a call
> other the futex_wait_requeue_pi(), the q.rt_waiter may be null. If so,
> this will result in an oops from the following call graph:
>
> futex_requeue()
> rt_mutex_start_proxy_lock()
> task_blocks_on_rt_mutex()
> waiter->task dereference
> OOPS
>
> We currently WARN_ON() if this is detected, clearly this is inadequate.
> If we detect a mispairing in futex_requeue(), bail out, seding -EINVAL to
> user-space.
>
> V2: Fix parenthesis warnings.
>
> Signed-off-by: Darren Hart <dvhltc@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> CC: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> CC: Dinakar Guniguntala <dino@xxxxxxxxxx>
> CC: John Stultz <johnstul@xxxxxxxxxx>
> ---
>
> kernel/futex.c | 11 +++++++++--
> 1 files changed, 9 insertions(+), 2 deletions(-)
>
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index df30983..4705d89 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1306,8 +1306,15 @@ retry_private:
> if (!match_futex(&this->key, &key1))
> continue;
>
> - WARN_ON(!requeue_pi && this->rt_waiter);
> - WARN_ON(requeue_pi && !this->rt_waiter);
> + /*
> + * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
> + * be paired with each other and no other futex ops.
> + */
> + if ((requeue_pi && !this->rt_waiter) ||
> + (!requeue_pi && this->rt_waiter)) {
> + ret = -EINVAL;
> + break;
> + }
>
> /*
> * Wake nr_wake waiters. For requeue_pi, if we acquired the
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