Messages in this thread | | | Date | Thu, 12 Sep 2013 16:32:00 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] kernel/futex.c: notice the return value after rt_mutex_finish_proxy_lock() fails |
| |
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.chen@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
| |