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SubjectRe: [PATCH] rt_mutex: correctly initialize lockdep in rt_mutex_init_proxy_locked
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On Sat, Jun 10, 2017 at 04:02:12PM +0200, Peter Zijlstra wrote:
> On Sat, Jun 10, 2017 at 02:48:04AM +0000, Levin, Alexander (Sasha Levin) wrote:
> > lockdep can't deal with NULL name or key, and doesn't do anything
> > with the lock when that happens.
>
> Not doing anything is 'right', the proxy stuff won't be lockdep tracked
> anyway. But yeah, the first thing is a wee bit of a problem, for it will
> trigger DEBUG_LOCKS_WARN_ON() and fully kill lockdep.

But don't we want pi_state->pi_mutex tracked by lockdep?

> Yeah, no need to do that; all we really need here is something like:
>
> ---
> kernel/locking/rtmutex-debug.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/locking/rtmutex-debug.c b/kernel/locking/rtmutex-debug.c
> index ac35e648b0e5..8dc647dc4b4b 100644
> --- a/kernel/locking/rtmutex-debug.c
> +++ b/kernel/locking/rtmutex-debug.c
> @@ -175,7 +175,8 @@ void debug_rt_mutex_init(struct rt_mutex *lock, const char *name, struct lock_cl
> lock->name = name;
>
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> - lockdep_init_map(&lock->dep_map, name, key, 0);
> + if (name && key)
> + lockdep_init_map(&lock->dep_map, name, key, 0);
> #endif
> }

I didn't want to do that because in later calls on that mutex we
will end up going into lockdep code, and I didn't think that doing
that without calling lockdep_init_map() initially was safe.

--

Thanks,
Sasha
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