* nan chen <nach...@gmail.com> wrote:
> 2013/1/25 Ingo Molnar <mi...@kernel.org>
>
> >
> > * nan chen <nach...@gmail.com> wrote:
> >
> > > 2013/1/25 Ingo Molnar <mi...@kernel.org>
> > >
> > > >
> > > > * Andrew Morton <a...@linux-foundation.org> wrote:
> > > >
> > > > > On Thu, 24 Jan 2013 17:22:45 +0800
> > > > > Yuanhan Liu <yuanhan....@linux.intel.com> wrote:
> > > > >
> > > > > > Use spin_[un]lock instead of arch_spin_[un]lock in mutex-debug.h so
> > > > > > that we can collect the lock statistics of spin_lock_mutex from
> > > > > > /proc/lock_stat.
> > > >
> > > > So, as per the discussion we don't want this patch, because we
> > > > are using raw locks there to keep mutex lockdep overhead low.
> > > > The value of lockdep-checking such a basic locking primitive is
> > > > minimal - it's rarely tweaked and if it breaks we won't have a
> > > > bootable kernel to begin with.
> > > >
> > > > So instead I suggested a different patch: adding a comment to
> > > > explain why we don't lockdep-cover the mutex code spinlocks.
> > > >
> > > > > 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); \
> > > >
> > > > Yes, I mentioned that yesterday, but we really don't want the
> > > > change to begin with.
> > > >
> > > > Thanks,
> > > >
> > > > Ingo
> > > >
> > >
> > > Hi,
> > >
> > > Looks like in mutex.h, it does not disable local interrupt.
> > > But why the code disable local interrupt in mutex-debug.h?
> >
> > To protect against preemption I suspect. preempt_disable() could
> > be used in the mutex-debug.h variant I suppose.
> >
> > Thanks,
> >
> > Ingo
> >
>
>
> spin_lock() itself already protects against preemption.
Yes, but mutex-debug.h does not use spin_lock(), it uses
arch_spin_lock():
#define spin_lock_mutex(lock, flags) \
do { \
struct mutex *l = container_of(lock, struct mutex, wait_lock); \
\
DEBUG_LOCKS_WARN_ON(in_interrupt()); \
local_irq_save(flags); \
arch_spin_lock(&(lock)->rlock.raw_lock);\
DEBUG_LOCKS_WARN_ON(l->magic != l); \
} while (0)
The original question was why mutex-debug.h (unmodified) uses
irq disabling.
Thanks,
Ingo
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