A frequent mode of operation is fanning out N tasks to execute in parallel, collating results, fanning out M tasks, rinse and repeat. This is also common to the notion of the async/sync kernel domain split. A barrier provides a mechanism by which all work queued after the barrier must wait (i.e. not be scheduled) until all work queued before the barrier is completed.

Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Shuah Khan shuahkh@osg.samsung.com Cc: Tejun Heo tj@kernel.org Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Andrew Morton akpm@linux-foundation.org Cc: Ingo Molnar mingo@kernel.org Cc: Kees Cook keescook@chromium.org Cc: Thomas Gleixner tglx@linutronix.de Cc: "Paul E. McKenney" paulmck@linux.vnet.ibm.com Cc: Dan Williams dan.j.williams@intel.com Cc: Andrey Ryabinin aryabinin@virtuozzo.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: Nikolay Aleksandrov nikolay@cumulusnetworks.com Cc: "David S. Miller" davem@davemloft.net Cc: "Peter Zijlstra (Intel)" peterz@infradead.org Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Cc: Andy Shevchenko andriy.shevchenko@linux.intel.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Alexander Potapenko glider@google.com Cc: linux-kernel@vger.kernel.org Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org --- include/linux/async.h | 4 ++++ kernel/async.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 64 insertions(+)

diff --git a/include/linux/async.h b/include/linux/async.h index 45d6c8323b60..64a090e3f24f 100644 --- a/include/linux/async.h +++ b/include/linux/async.h @@ -26,6 +26,7 @@ struct async_work {

struct async_domain { struct list_head pending; + struct kfence *barrier; unsigned registered:1; };

@@ -59,6 +60,9 @@ extern void async_synchronize_cookie(async_cookie_t cookie); extern void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain);

+extern void async_barrier(void); +extern void async_barrier_domain(struct async_domain *domain); + extern bool current_is_async(void);

extern struct async_work * diff --git a/kernel/async.c b/kernel/async.c index 83007c39a113..a22945f4b4c4 100644 --- a/kernel/async.c +++ b/kernel/async.c @@ -724,6 +724,12 @@ struct async_work *async_work_create(async_func_t func, void *data, gfp_t gfp) } EXPORT_SYMBOL_GPL(async_work_create);

+static void async_barrier_delete(struct async_domain *domain) +{ + kfence_put(domain->barrier); + domain->barrier = NULL; +} + async_cookie_t queue_async_work(struct async_domain *domain, struct async_work *work, gfp_t gfp) @@ -744,6 +750,9 @@ async_cookie_t queue_async_work(struct async_domain *domain, async_pending_count++; spin_unlock_irqrestore(&async_lock, flags);

+ if (!kfence_add(&entry->base.fence, domain->barrier, gfp)) + async_barrier_delete(domain); + /* mark that this task has queued an async job, used by module init */ current->flags |= PF_USED_ASYNC;

@@ -811,6 +820,55 @@ async_cookie_t async_schedule_domain(async_func_t func, void *data, } EXPORT_SYMBOL_GPL(async_schedule_domain);

+static struct kfence * __async_barrier_create(struct async_domain *domain) +{ + struct kfence *fence; + struct async_entry *entry; + unsigned long flags; + int ret; + + fence = kfence_create(GFP_KERNEL); + if (!fence) + goto out_sync; + + ret = 0; + spin_lock_irqsave(&async_lock, flags); + list_for_each_entry(entry, &domain->pending, pending_link[0]) { + ret |= kfence_add(fence, &entry->base.fence, GFP_ATOMIC); + if (ret < 0) + break; + } + spin_unlock_irqrestore(&async_lock, flags); + if (ret <= 0) + goto out_put; + + kfence_add(fence, domain->barrier, GFP_KERNEL); + kfence_signal(fence); + return fence; + +out_put: + kfence_signal(fence); + kfence_put(fence); +out_sync: + async_synchronize_full_domain(domain); + return NULL; +} + +void async_barrier(void) +{ + async_barrier_domain(&async_dfl_domain); +} +EXPORT_SYMBOL_GPL(async_barrier); + +void async_barrier_domain(struct async_domain *domain) +{ + struct kfence *barrier = __async_barrier_create(domain); + + kfence_put(domain->barrier); + domain->barrier = barrier; +} +EXPORT_SYMBOL_GPL(async_barrier_domain); + /** * async_synchronize_full - synchronize all asynchronous function calls * @@ -834,6 +892,8 @@ EXPORT_SYMBOL_GPL(async_synchronize_full); void async_unregister_domain(struct async_domain *domain) { WARN_ON(!list_empty(&domain->pending)); + + async_barrier_delete(domain); domain->registered = 0; } EXPORT_SYMBOL_GPL(async_unregister_domain);