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SubjectRe: [BUG] futex_unlock_pi() hurts my brain and may cause application deadlock
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On Thu, 2007-05-31 at 16:55 +0200, Ingo Molnar wrote:
> * john stultz <johnstul@us.ibm.com> wrote:
>
> > > > --- a/kernel/futex.c
> > > > +++ b/kernel/futex.c
> > > > @@ -2011,6 +2011,7 @@ pi_faulted:
> > > > attempt);
> > > > if (ret)
> > > > goto out_unlock;
> > > > + uval = 0;
> > > > goto retry_locked;
> > >
> > > this looks good to me. Oleg has posted a few more fixes as well -
> > > have you tried those too?
> >
> > Do you have a URL or subject line for the discussion? I'll take a look
> > and give them a whirl.
>
> i meant to say Alexey, not Oleg :-) Here's the thread:
>
> http://lkml.org/lkml/2007/5/7/129
>
> i've Cc:-ed Alexey too.

I haven't had a chance to run it, but reviewing at Alexey's changes,
they do not look to be sufficient to the issue we were hitting. We still
need to clear uval to avoid -EFAULT &'ing w/ FUTEX_OWNER_DIED.


Here's the patch against -rt9 (which also contains Alexey's fix)


diff -rup 2.6-rt/kernel/futex.c 2.6-rtnew/kernel/futex.c
--- 2.6-rt/kernel/futex.c 2007-05-31 06:38:00.000000000 -0500
+++ 2.6-rtnew/kernel/futex.c 2007-05-31 06:43:08.000000000 -0500
@@ -1954,6 +1954,7 @@ pi_faulted:
ret = -EFAULT;
goto out_unlock;
}
+ uval = 0;
goto retry_locked;
}

@@ -3503,6 +3504,7 @@ pi_faulted:
ret = -EFAULT;
goto out_unlock;
}
+ uval = 0;
goto retry_locked;
}



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