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    SubjectRe: rt_mutex: restore wait_lock init in __rt_mutex_init
    On 07/27/2011 11:37 AM, Thomas Gleixner wrote:
    > On Wed, 27 Jul 2011, Darren Hart wrote:
    >
    >> Without the raw_spin_lock_init(), the wait_lock does not get properly
    >> initialized with CONFIG_DEBUG_SPINLOCK. This can manifest in a BUG() in the
    >> futex requeue_pi path when the pi_state->pi_mutex->wait_lock fails the magic
    >> test in rt_mutex_start_proxy_lock()->raw_spin_lock(&lock->wait_lock).
    > That's actively wrong. You reinitialize the lock for all other cases
    > which call this via rt_mutex_init(). There is a reason why I moved the
    > spin lock initializer out of __rt_mutex_init() into
    > rt_mutex_init(). The lock name stuff for lockdep ends up to be
    > "lock->wait_lock" for all rt_mutexes, which is pretty useless when you
    > have to analyze a lockdep splat. Thanks for finding it nevertheless.
    >
    > So the correct fix is:
    >
    > Index: linux-2.6/kernel/rtmutex.c
    > ===================================================================
    > --- linux-2.6.orig/kernel/rtmutex.c
    > +++ linux-2.6/kernel/rtmutex.c
    > @@ -1296,7 +1296,7 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init);
    > void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
    > struct task_struct *proxy_owner)
    > {
    > - __rt_mutex_init(lock, NULL);
    > + rt_mutex_init(lock);
    > debug_rt_mutex_proxy_lock(lock, proxy_owner);
    > rt_mutex_set_owner(lock, proxy_owner);
    > rt_mutex_deadlock_account_lock(lock, proxy_owner);
    >
    >
    Seems to work. I no longer get a warning from pulseaudio either.
    Also darren, at least on fedora 15 glibc supports requeue_pi.
    support for that is in nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_*.S

    Cheers,
    Maarten


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