Messages in this thread |  | | | Subject | Re: [PATCH] kthread_worker: Initialize dynamically allocated spinlock properly for lockdep | | From | Andy Walls <> | | Date | Mon, 20 Dec 2010 12:16:27 -0500 |
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On Mon, 2010-12-20 at 17:28 +0800, Yong Zhang wrote: > On Mon, Dec 20, 2010 at 3:07 PM, Yong Zhang <yong.zhang0@gmail.com> wrote: > > On Sun, Dec 19, 2010 at 8:49 PM, Andy Walls <awalls@md.metrocast.net> wrote: > >> init_kthread_worker(), via KTHREAD_WORKER_INIT(), used an > >> initializer for static spin_lock objects, SPIN_LOCK_UNLOCKED, on > >> a dynamically allocated kthread_worker object's internal spinlock_t. > >> This causes lockdep to gripe: > >> > >> INFO: trying to register non-static key. > >> the code is fine but needs lockdep annotation. > >> turning off the locking correctness validator. > >> > >> To keep lockdep happy, use spin_lock_init() for dynamically > >> allocated kthread_worker objects' internal spinlock_t. > >> > >> Reported-by: Nicolas <nicolas.mailhot@laposte.net> > >> Signed-off-by: Andy Walls <awalls@md.metrocast.net> > >> > >> Cc: Tejun Heo <tj@kernel.org> > >> Cc: Jarod Wilson <jarod@redhat.com> > >> Cc: Ingo Molnar <mingo@redhat.com> > >> Cc: Mauro Carvalho Chehab <mchehab@redhat.com> > >> Cc: Hans Verkuil <hverkuil@xs4all.nl>
> > This will make different kthead_worker->lock initialized with one same > > key.
Well, that wouldn't be very useful. :P
> > So we should put the real initializer to kernel/kthread.c > > and make init_kthread_worker() to be a MACRO.
Sounds OK to me. I'm not a lockdep expert and I made my initial patch with the sole intention of making this bugzilla report go away:
https://bugzilla.redhat.com/show_bug.cgi?id=662384
> untested patch is here. Andy/Nicolas, is it ok for you?
No, see my comments below.
> --- > Subject: [PATCH] kthread_work: Make lockdep happy > > spinlock in kthread_worker and wait_queue_head in kthread_work > both should be lockdep annotated. > So change the interface to make it suiltable for CONFIG_LOCKDEP. > > Signed-off-by: Yong Zhang <yong.zhang0@gmail.com> > --- > I'm not sure if it's possible to define a worker on stack? > So I left DEFINE_KTHREAD_WORKER() untouched. > > include/linux/kthread.h | 37 +++++++++++++++++++++++++++---------- > kernel/kthread.c | 9 +++++++++ > 2 files changed, 36 insertions(+), 10 deletions(-) > > diff --git a/include/linux/kthread.h b/include/linux/kthread.h > index 685ea65..5d516b3 100644 > --- a/include/linux/kthread.h > +++ b/include/linux/kthread.h > @@ -75,22 +75,39 @@ struct kthread_work { > .flushing = ATOMIC_INIT(0), \ > } > > +/* Is it possible to define a worker on stack? */
This comment doesn't help a developer decide if this interface is OK to use.
If there is an alternate preferred API for instantiating 1 (or more) thread(s) to handle work objects off of the stack, then the comment should point the reader to that API (e.g. singlethread_workqueue).
To answer the question in the comment:
It is possible to allocate a kthread worker off of the stack, but IMO it has little advantage over a singlethread_workqueue allocated off of the stack.
ivtv only needed the kthread_worker API, because it has some deferred work with tight timing constraints. ivtv sets the kthread_worker to SCHED_FIFO scheduling for ivtv work, which couldn't be done on a workqueue thread with the updated singlethread_workqueue implementation. Note that ivtv does *not* allocate its kthread worker off of the stack.
> #define DEFINE_KTHREAD_WORKER(worker) \ > struct kthread_worker worker = KTHREAD_WORKER_INIT(worker) > > #define DEFINE_KTHREAD_WORK(work, fn) \ > struct kthread_work work = KTHREAD_WORK_INIT(work, fn) > > -static inline void init_kthread_worker(struct kthread_worker *worker) > -{ > - *worker = (struct kthread_worker)KTHREAD_WORKER_INIT(*worker); > -} > - > -static inline void init_kthread_work(struct kthread_work *work, > - kthread_work_func_t fn) > -{ > - *work = (struct kthread_work)KTHREAD_WORK_INIT(*work, fn); > -} > +#ifdef CONFIG_LOCKDEP > +# define KTHREAD_WORK_INIT_ONSTACK(work, fn) \ > + ({init_kthread_work((&work), fn); work}) > +# define DEFINE_KTHREAD_WORK_ONSTACK(work, fn) \ > + struct kthread_work work = KTHREAD_WORK_INIT_ONSTACK(work, fn) > +#else > +# define DEFINE_KTHREAD_WORK_ONSTACK(work, fn) DEFINE_KTHREAD_WORK(work, fn) > +#endif > + > +extern void __init_kthread_worker(struct kthread_worker *worker, > + struct lock_class_key *key); > + > +#define init_kthread_worker(worker) \ > + do { \ > + static struct lock_class_key __key; \ > + __init_kthread_worker((worker), &__key); \ > + } while (0) > + > +#define init_kthread_work(work, fn) \ > + do { \ > + memset((work), 0, sizeof(struct kthread_work)); \ > + INIT_LIST_HEAD(&(work)->node); \ > + (work)->func = (fn); \ > + init_waitqueue_head(&(work)->done); \ > + (work)->flushing = ATOMIC_INIT(0); \ > + } while (0) > > int kthread_worker_fn(void *worker_ptr); > > diff --git a/kernel/kthread.c b/kernel/kthread.c > index 2dc3786..fae2eff 100644 > --- a/kernel/kthread.c > +++ b/kernel/kthread.c > @@ -265,6 +265,15 @@ int kthreadd(void *unused) > return 0; > } > > +void __init_kthread_worker(struct kthread_worker *worker, > + struct lock_class_key *key) > +{ > + spin_lock_init(&worker->lock); > + lockdep_set_class(&worker->lock, key); > + INIT_LIST_HEAD(&worker->work_list); > + worker->task == NULL; ^^ | GCC should have griped, "Statement with no effect," or something similar. (Did it?) Regards, Andy
> +} > + > /** > * kthread_worker_fn - kthread function to process kthread_worker > * @worker_ptr: pointer to initialized kthread_worker > -- > 1.7.0.4
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