Re: robust futex heap support patch

[david singleton <dsingleton@mvista.com>]

On Nov 26, 2005, at 5:31 AM, Ingo Molnar wrote:

> * david singleton <dsingleton@mvista.com> wrote:
>
> > There is a new patch, patch-2.6.14-rt15-rf1, that adds support for
> > robust and priority inheriting pthread_mutexes on the 'heap'.
>
> we need to go a bit slower. For now i had to remove robust-futexes from
> the -rt17 release because they broke normal (non-robust) futex support
> in -rt15. A simple mozilla startup would hang... Please send fixes
> against -rt16 and i'll try to re-add the robust futexes patch later on.
> You can find -rt16 at:

whoops, sorry.

Here's he piece that broke regular futexes.  Futex wake doesn't
need to check to see if the robust list is null or not.

Index: linux-2.6.14/kernel/futex.c
===================================================================
--- linux-2.6.14.orig/kernel/futex.c
+++ linux-2.6.14/kernel/futex.c
@@ -323,10 +323,6 @@ static int futex_wake(unsigned long uadd
        ret = get_futex_key(uaddr, &key, &head, &sem);
        if (unlikely(ret != 0))
                goto out;
-       if (head == NULL) {
-               ret = -EINVAL;
-               goto out;
-       }

        bh = hash_futex(&key);
        spin_lock(&bh->lock);


Let me get the build fixed and add a new test for myself.  I'll start  
running
this on my desktop to do builds, run mozilla and firefox, and generally
do all my normal work.

David
>   
> http://people.redhat.com/mingo/realtime-preempt/older/patch-2.6.14- 
> rt16
>
> > The previous patches only supported either file based pthread_mutexes
> > or mmapped anonymous memory based pthread_mutexes.  This patch allows
> > pthread_mutexes to be 'malloc'ed while using the
> > PTHREAD_MUTEX_ROBUST_NP attribute or PTHREAD_PRIO_INHERIT attribute.
> >
> > The patch can be found at:
> >
> > http://source.mvista.com/~dsingleton
>
> this patch looks much cleaner than the earlier one, but there's one  
> more
> step to go: now that we've got the futex_head in every vma, why not  
> hang
> all robust futexes to the vma, and thus get rid of ->robust_list and
> ->robust_sem from struct address_space?
>
> 	Ingo

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