On Tue, 20 Aug 2013, Chen Gang wrote:
> rt_mutex_finish_proxy_lock() can return failure code (e.g. -EINTR,
> -ETIMEDOUT).
>
> Original implementation has already noticed about it, but not check it
> before next work.
>
> Also let coments within 80 columns to pass "./scripts/checkpatch.pl".
>
>
> Signed-off-by: Chen Gang <gang.c...@asianux.com>
> ---
> kernel/futex.c | 30 ++++++++++++++++--------------
> 1 files changed, 16 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index c3a1a55..1a94e7d 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -2373,21 +2373,23 @@ static int futex_wait_requeue_pi(u32 __user *uaddr,
> unsigned int flags,
> ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
> debug_rt_mutex_free_waiter(&rt_waiter);
>
> - spin_lock(q.lock_ptr);
> - /*
> - * Fixup the pi_state owner and possibly acquire the lock if we
> - * haven't already.
> - */
> - res = fixup_owner(uaddr2, &q, !ret);
> - /*
> - * If fixup_owner() returned an error, proprogate that. If it
> - * acquired the lock, clear -ETIMEDOUT or -EINTR.
> - */
> - if (res)
> - ret = (res < 0) ? res : 0;
> + if (!ret) {
Again. This is completely wrong!
We MUST call fixup_owner even if finish_proxy_lock() returned with an
error code. Simply because finish_proxy_lock() is called outside of
the spin_lock(q.lock_ptr) region and another thread might have
modified the futex state. So we need to handle the corner cases
otherwise we might leave the futex in some undefined state.
You're reintroducing a hard to decode bug, which got analyzed and
fixed in futex_lock_pi() years ago. See the history for the
explanation.
Sigh.
tglx
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