Messages in this thread | | | Date | Wed, 10 Jul 2019 21:15:49 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH] locking/mutex: Test for initialized mutex |
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On 2019-07-10 17:50:54 [+0100], Will Deacon wrote: > On Wed, Jul 03, 2019 at 11:21:26AM +0200, Sebastian Andrzej Siewior wrote: > > An uninitialized/ zeroed mutex will go unnoticed because there is no > > check for it. There is a magic check in the unlock's slowpath path which > > might go unnoticed if the unlock happens in the fastpath. > > > > Add a ->magic check early in the mutex_lock() and mutex_trylock() path. > > > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > > --- > > Nothing screamed during uninitialized usage of init_mm's context->lock > > https://git.kernel.org/tip/32232b350d7cd93cdc65fe5a453e6a40b539e9f9 > > > > kernel/locking/mutex.c | 11 ++++++++++- > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > > index 0c601ae072b3f..fb1f6f1e1cc61 100644 > > --- a/kernel/locking/mutex.c > > +++ b/kernel/locking/mutex.c > > @@ -908,6 +908,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, > > > > might_sleep(); > > > > +#ifdef CONFIG_DEBUG_MUTEXES > > + DEBUG_LOCKS_WARN_ON(lock->magic != lock); > > +#endif > > Why do we need to check this so early, or could we move it into > debug_mutex_lock_common() instead?
debug_mutex_lock_common() is too late. A few lines later, before "preempt_disable()" would be possible. After that, there is __mutex_trylock() which would succeed so you don't catch the uninitialized case. By the time you get to debug_mutex_lock_common() you need contention and then acquire ->wait_lock which should complain about missing magic.
> Will
Sebastian
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