On Thu, 24 Jan 2013 19:50:57 -0500
Steven Rostedt <rost...@goodmis.org> wrote:
> These changes are fine and wont hurt -rt. But thanks for think about
> us :-)
Thanks (tglx) for writing a useful changelog ;)
> >
> > Also, I believe your patch permits this cleanup:
> >
> > --- a/kernel/mutex-debug.h~mutex-use-spin_lock-instead-of-arch_spin_lock-fix
> > +++ a/kernel/mutex-debug.h
> > @@ -42,14 +42,12 @@ static inline void mutex_clear_owner(str
> > struct mutex *l = container_of(lock, struct mutex, wait_lock); \
> > \
> > DEBUG_LOCKS_WARN_ON(in_interrupt()); \
> > - local_irq_save(flags); \
> > - spin_lock(lock); \
> > + spin_lock_irqsave(lock, flags); \
> > DEBUG_LOCKS_WARN_ON(l->magic != l); \
> > } while (0)
> >
> > #define spin_unlock_mutex(lock, flags) \
> > do { \
> > - spin_unlock(lock); \
> > - local_irq_restore(flags); \
> > + spin_unlock_irqrestore(lock, flags); \
> > preempt_check_resched(); \
> > } while (0)
>
> Actually this perhaps hurts lockdep. We want to keep the
> arch_spin_(un)lock() versions because each spin_lock() and spin_unlock()
> needs to be verified by lockdep. Lockdep also verifies mutex locks. But
> with this change, for every mutex, it's going to also analyze a
> spin_lock and spin_unlock twice each (one for mutex lock and one for
> unlock). As this is just locking the mutex internals, it may not be
> necessary to debug it via lockdep. Hence we probably want to keep the
> arch_* version.
In what way is this actually a problem? lockdep will have more work to
do (and given the frequency of mutex_lock/unlock, that overhead may be
significant). Anything else?
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