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SubjectRe: [PATCH 1/2] lockdep: finer-grained completion key for kthread
On Wed, Nov 29, 2017 at 04:41:44PM +0100, Daniel Vetter wrote:
> Ideally we'd create the key through a macro at the real callers and
> pass it all the way down. This would give us better coverage for cases
> where a bunch of kthreads are created for the same thing.
> But this gets the job done meanwhile and unblocks our CI. Refining
> later on is always possible.
>
> v2:
> - make it compile
> - use the right map (Tvrtko)
>
> v3:
>
> lockdep insist on a static key, so the cheap way didn't work. Wire
> 2 keys through all the callers.
>
> I didn't extend this up to alloc_workqueue because the
> lockdep_invariant_state() call should separate the work functions from
> the workqueue kthread logic and prevent cross-release state from
> leaking between unrelated work queues that happen to reuse the same
> kthreads.
>
> v4: CI found more compile fail :-/
>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Marta Lofstedt <marta.lofstedt@intel.com>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=103950
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Any comments on this issue here? Is there a real patch we should use
instead of this quick hack?

As mentioned in the cover letter, I don't really have much clue, this is
more an elaborate bug report than anything like a real code submission :-)

Thanks, Daniel

> ---
> include/linux/kthread.h | 48 ++++++++++++++++++++++++++++-----
> kernel/kthread.c | 70 ++++++++++++++++++++++++++++++++++---------------
> 2 files changed, 90 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/kthread.h b/include/linux/kthread.h
> index c1961761311d..7a9463f0be5c 100644
> --- a/include/linux/kthread.h
> +++ b/include/linux/kthread.h
> @@ -6,10 +6,12 @@
> #include <linux/sched.h>
> #include <linux/cgroup.h>
>
> -__printf(4, 5)
> -struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
> +__printf(6, 7)
> +struct task_struct *_kthread_create_on_node(int (*threadfn)(void *data),
> void *data,
> int node,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char namefmt[], ...);
>
> /**
> @@ -25,12 +27,27 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
> */
> #define kthread_create(threadfn, data, namefmt, arg...) \
> kthread_create_on_node(threadfn, data, NUMA_NO_NODE, namefmt, ##arg)
> +#define kthread_create_on_node(threadfn, data, node, namefmt, arg...) \
> +({ \
> + static struct lock_class_key __exited_key, __parked_key; \
> + _kthread_create_on_node(threadfn, data, node, &__exited_key, \
> + &__parked_key, namefmt, ##arg); \
> +})
>
>
> -struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
> +struct task_struct *_kthread_create_on_cpu(int (*threadfn)(void *data),
> void *data,
> unsigned int cpu,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char *namefmt);
> +#define kthread_create_on_cpu(threadfn, data, cpu, namefmt) \
> +({ \
> + static struct lock_class_key __exited_key, __parked_key; \
> + _kthread_create_on_cpu(threadfn, data, cpu, &__exited_key,\
> + &__parked_key, namefmt); \
> +})
> +
>
> /**
> * kthread_run - create and wake a thread.
> @@ -171,13 +188,30 @@ extern void __kthread_init_worker(struct kthread_worker *worker,
>
> int kthread_worker_fn(void *worker_ptr);
>
> -__printf(2, 3)
> +__printf(4, 5)
> struct kthread_worker *
> -kthread_create_worker(unsigned int flags, const char namefmt[], ...);
> +_kthread_create_worker(unsigned int flags,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> + const char namefmt[], ...);
> +#define kthread_create_worker(flags, namefmt...) \
> +({ \
> + static struct lock_class_key __exited_key, __parked_key; \
> + _kthread_create_worker(flags, &__exited_key, &__parked_key, \
> + ##namefmt); \
> +})
>
> -__printf(3, 4) struct kthread_worker *
> -kthread_create_worker_on_cpu(int cpu, unsigned int flags,
> +__printf(5, 6) struct kthread_worker *
> +_kthread_create_worker_on_cpu(int cpu, unsigned int flags,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char namefmt[], ...);
> +#define kthread_create_worker_on_cpu(cpu, flags, namefmt...) \
> +({ \
> + static struct lock_class_key __exited_key, __parked_key; \
> + _kthread_create_worker_on_cpu(cpu, flags, &__exited_key, &__parked_key,\
> + ##namefmt); \
> +})
>
> bool kthread_queue_work(struct kthread_worker *worker,
> struct kthread_work *work);
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index cd50e99202b0..9022806818fc 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -32,6 +32,7 @@ struct kthread_create_info
> int (*threadfn)(void *data);
> void *data;
> int node;
> + struct lock_class_key *exited_key, *parked_key;
>
> /* Result passed back to kthread_create() from kthreadd. */
> struct task_struct *result;
> @@ -221,8 +222,17 @@ static int kthread(void *_create)
> }
>
> self->data = data;
> - init_completion(&self->exited);
> - init_completion(&self->parked);
> + /* these two completions are shared with all kthread, which is bonghist
> + * imo */
> + lockdep_init_map_crosslock(&self->exited.map.map,
> + "(kthread completion)->exited",
> + create->exited_key, 0);
> + init_completion_map(&self->exited, &self->exited.map.map);
> + lockdep_init_map_crosslock(&self->parked.map.map,
> + "(kthread completion)->parked",
> + create->parked_key, 0);
> + init_completion_map(&self->parked, &self->exited.map.map);
> +
> current->vfork_done = &self->exited;
>
> /* OK, tell user we're spawned, wait for stop or wakeup */
> @@ -272,9 +282,11 @@ static void create_kthread(struct kthread_create_info *create)
> }
> }
>
> -static __printf(4, 0)
> +static __printf(6, 0)
> struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
> void *data, int node,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char namefmt[],
> va_list args)
> {
> @@ -289,6 +301,8 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
> create->data = data;
> create->node = node;
> create->done = &done;
> + create->exited_key = exited_key;
> + create->parked_key = parked_key;
>
> spin_lock(&kthread_create_lock);
> list_add_tail(&create->list, &kthread_create_list);
> @@ -353,21 +367,24 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
> *
> * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
> */
> -struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
> - void *data, int node,
> - const char namefmt[],
> - ...)
> +struct task_struct *_kthread_create_on_node(int (*threadfn)(void *data),
> + void *data, int node,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> + const char namefmt[],
> + ...)
> {
> struct task_struct *task;
> va_list args;
>
> va_start(args, namefmt);
> - task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
> + task = __kthread_create_on_node(threadfn, data, node,
> + exited_key, parked_key, namefmt, args);
> va_end(args);
>
> return task;
> }
> -EXPORT_SYMBOL(kthread_create_on_node);
> +EXPORT_SYMBOL(_kthread_create_on_node);
>
> static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, long state)
> {
> @@ -421,14 +438,16 @@ EXPORT_SYMBOL(kthread_bind);
> * Description: This helper function creates and names a kernel thread
> * The thread will be woken and put into park mode.
> */
> -struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
> +struct task_struct *_kthread_create_on_cpu(int (*threadfn)(void *data),
> void *data, unsigned int cpu,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char *namefmt)
> {
> struct task_struct *p;
>
> - p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
> - cpu);
> + p = _kthread_create_on_node(threadfn, data, cpu_to_node(cpu),
> + exited_key, parked_key, namefmt, cpu);
> if (IS_ERR(p))
> return p;
> kthread_bind(p, cpu);
> @@ -649,8 +668,10 @@ int kthread_worker_fn(void *worker_ptr)
> }
> EXPORT_SYMBOL_GPL(kthread_worker_fn);
>
> -static __printf(3, 0) struct kthread_worker *
> +static __printf(5, 0) struct kthread_worker *
> __kthread_create_worker(int cpu, unsigned int flags,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char namefmt[], va_list args)
> {
> struct kthread_worker *worker;
> @@ -666,8 +687,8 @@ __kthread_create_worker(int cpu, unsigned int flags,
> if (cpu >= 0)
> node = cpu_to_node(cpu);
>
> - task = __kthread_create_on_node(kthread_worker_fn, worker,
> - node, namefmt, args);
> + task = __kthread_create_on_node(kthread_worker_fn, worker, node,
> + exited_key, parked_key, namefmt, args);
> if (IS_ERR(task))
> goto fail_task;
>
> @@ -694,18 +715,22 @@ __kthread_create_worker(int cpu, unsigned int flags,
> * when the worker was SIGKILLed.
> */
> struct kthread_worker *
> -kthread_create_worker(unsigned int flags, const char namefmt[], ...)
> +_kthread_create_worker(unsigned int flags,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> + const char namefmt[], ...)
> {
> struct kthread_worker *worker;
> va_list args;
>
> va_start(args, namefmt);
> - worker = __kthread_create_worker(-1, flags, namefmt, args);
> + worker = __kthread_create_worker(-1, flags, exited_key, parked_key,
> + namefmt, args);
> va_end(args);
>
> return worker;
> }
> -EXPORT_SYMBOL(kthread_create_worker);
> +EXPORT_SYMBOL(_kthread_create_worker);
>
> /**
> * kthread_create_worker_on_cpu - create a kthread worker and bind it
> @@ -725,19 +750,22 @@ EXPORT_SYMBOL(kthread_create_worker);
> * when the worker was SIGKILLed.
> */
> struct kthread_worker *
> -kthread_create_worker_on_cpu(int cpu, unsigned int flags,
> +_kthread_create_worker_on_cpu(int cpu, unsigned int flags,
> + struct lock_class_key *exited_key,
> + struct lock_class_key *parked_key,
> const char namefmt[], ...)
> {
> struct kthread_worker *worker;
> va_list args;
>
> va_start(args, namefmt);
> - worker = __kthread_create_worker(cpu, flags, namefmt, args);
> + worker = __kthread_create_worker(cpu, flags, exited_key, parked_key,
> + namefmt, args);
> va_end(args);
>
> return worker;
> }
> -EXPORT_SYMBOL(kthread_create_worker_on_cpu);
> +EXPORT_SYMBOL(_kthread_create_worker_on_cpu);
>
> /*
> * Returns true when the work could not be queued at the moment.
> --
> 2.15.0
>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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