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Message-ID: <1292865387.9445.28.camel@morgan.silverblock.net>
Date: Mon, 20 Dec 2010 12:16:27 -0500
From: Andy Walls <awalls@...metrocast.net>
To: Yong Zhang <yong.zhang0@...il.com>
Cc: linux-kernel@...r.kernel.org, nicolas.mailhot@...oste.net,
Tejun Heo <tj@...nel.org>, Jarod Wilson <jarod@...hat.com>,
Ingo Molnar <mingo@...hat.com>,
Mauro Carvalho Chehab <mchehab@...hat.com>,
Hans Verkuil <hverkuil@...all.nl>
Subject: Re: [PATCH] kthread_worker: Initialize dynamically allocated
spinlock properly for lockdep
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@...il.com> wrote:
> > On Sun, Dec 19, 2010 at 8:49 PM, Andy Walls <awalls@...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@...oste.net>
> >> Signed-off-by: Andy Walls <awalls@...metrocast.net>
> >>
> >> Cc: Tejun Heo <tj@...nel.org>
> >> Cc: Jarod Wilson <jarod@...hat.com>
> >> Cc: Ingo Molnar <mingo@...hat.com>
> >> Cc: Mauro Carvalho Chehab <mchehab@...hat.com>
> >> Cc: Hans Verkuil <hverkuil@...all.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@...il.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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